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C Programming Code Examples

C > Small Programs Code Examples

Print ip, email addressess or urls found in text

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/* Print ip, email addressess or urls found in text */ #include <stdio.h> #include <regex.h> #include <ctype.h> #include <getopt.h> #include <stdlib.h> #include <string.h> #include <locale.h> #include <sys/types.h> #define PACKAGE "miep" #define VERSION "1.0.0" #define IPEXPR "([0-9]{1,3})\\.([0-9]{1,3})\\.([0-9]{1,3})\\.([0-9]{1,3})" #define EMEXPR ".*@.*\\.([a-zA-Z]{1,3})$" #define UREXPR "(href|src)=" void print_ipadd(FILE *fp); void print_email(FILE *fp); void print_url(FILE *fp); void print_help(int exval); int main(int argc, char *argv[]) { FILE *fp = stdin; int opt = 0; int em_set = 0; int ip_set = 0; int ur_set = 0; setlocale(LC_ALL, ""); while((opt = getopt(argc, argv, "hvieu")) != -1) { switch(opt) { case 'h': print_help(0); break; case 'v': fprintf(stdout, "%s %s\n", PACKAGE, VERSION); exit(0); break; case 'i': ip_set = 1; break; case 'e': em_set = 1; break; case 'u': ur_set = 1; break; case '?': fprintf(stderr, "%s: Error: No such option `%c'\n\n", PACKAGE, optopt); print_help(1); break; } /* switch */ } /* while */ if(argc == 1 || (ip_set == 0 && em_set == 0 && ur_set == 0)) print_help(1); if((optind - argc) == 0) { if(em_set == 1) print_email(fp); else if(ip_set == 1) print_ipadd(fp); else print_url(fp); } else { /* loop over remaining args [files] */ for(; optind < argc; optind++) { if(freopen(argv[optind], "r", fp) == NULL) { perror(argv[optind]); continue; } if(em_set == 1) print_email(fp); else if(ip_set == 1) print_ipadd(fp); else print_url(fp); } /* for */ } /* else */ fclose(fp); return 0; } void print_ipadd(FILE *fp) { char line[1024]; char *address = NULL; char delim[] = ",:;`/\"+-_(){}[]<>*&^%$#@!?~/|\\= \t\r\n"; int retval = 0; regex_t re; if(regcomp(&re, IPEXPR, REG_EXTENDED) != 0) return; while((fgets(line, 1024, fp)) != NULL) { if(strchr(line, '.') == NULL) continue; address = strtok(line, delim); while(address != NULL) { if(strlen(address) <= 15) if((retval = regexec(&re, address, 0, NULL, 0)) == 0) printf("%s\n", address); address = strtok(NULL, delim); } /* while */ } /* while */ } /* print_ipadd */ void print_email(FILE *fp) { char address[256]; char line[1024]; char *ptr1 = NULL; char *ptr2 = NULL; int retval = 0; regex_t re; if(regcomp(&re, EMEXPR, REG_EXTENDED) != 0) return; while((fgets(line, 1024, fp)) != NULL) { if(strchr(line, '@') == NULL && strchr(line, '.') == NULL) continue; for(ptr1 = line, ptr2 = address; *ptr1; ptr1++) { if(isalpha(*ptr1) || isdigit(*ptr1) || strchr("[email protected]", *ptr1) != NULL) *ptr2++ = *ptr1; else { *ptr2 = '\0'; if(strlen(address) >= 6 && strchr(address, '@') != NULL && strchr(address, '.') != NULL) if((retval = regexec(&re, address, 0, NULL, 0)) == 0) printf("%s\n", address); ptr2 = address; } /* else */ } /* for */ } /* while */ } /* print_email */ void print_url(FILE *fp) { char line[1024]; char delim[] = "<> \t\n"; char *url = NULL; int retval = 0; regex_t re; if(regcomp(&re, UREXPR, REG_ICASE|REG_EXTENDED) != 0) return; while((fgets(line, 1024, fp)) != NULL) { url = strtok(line, delim); while(url != NULL) { if((retval = regexec(&re, url, 0, NULL, 0)) == 0) printf("%s\n", url); url = strtok(NULL, delim); } /* while */ } /* while */ } /* print_url */ void print_help(int exval) { printf("%s,%s print e-mail, urls or ip addresses from in textdata\n", PACKAGE, VERSION); printf("%s [-h] [-v] [-i] [-e] [-u] FILE...\n\n", PACKAGE); printf(" -h print this help and exit\n"); printf(" -v print version and exit\n\n"); printf(" -i print ip addresses\n"); printf(" -e print e-mail addresses\n"); printf(" -u print urls\n\n"); exit(exval); }
strchr() Function in C
Locate first occurrence of character in string. Search for a given character in a string. Returns a pointer to the first occurrence of character in the C string str. The terminating null-character is considered part of the C string. Therefore, it can also be located in order to retrieve a pointer to the end of a string. The strchr() function returns a pointer to the first occurrence of the character value character in the string addressed by str. If there is no such character in the string, strchr() returns a null pointer. If character is a null character ('\0'), then the return value points to the terminator character of the string addressed by str.
Syntax for strchr() Function in C
#include <string.h> const char * strchr ( const char * str, int character ); char * strchr ( char * str, int character );
str
C string
character
Character to be located. It is passed as its int promotion, but it is internally converted back to char for the comparison. Function returns a pointer to the first occurrence of character in str. If the character is not found, the function returns a null pointer.
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/* get first occurrence of character in string by strchr() string function code example */ #include <stdio.h> #include <string.h> int main () { char string[55] ="This is a string for testing"; char *p; int k = 1; p = strchr (string,'i'); while (p!=NULL) { printf ("Character i found at position %d\n",p-string+1); printf ("Occurrence of character \"i\" : %d \n",k); printf ("Occurrence of character \"i\" in \"%s\" is \"%s" \ "\"\n",string, p); p=strchr(p+1,'i'); k++; } return 0; }
strtok() Function in C
Split string into tokens. A sequence of calls to this function split str into tokens, which are sequences of contiguous characters separated by any of the characters that are part of delimiters. On a first call, the function expects a C string as argument for str, whose first character is used as the starting location to scan for tokens. In subsequent calls, the function expects a null pointer and uses the position right after the end of the last token as the new starting location for scanning.
Syntax for strtok() Function in C
#include <string.h> char * strtok ( char * str, const char * delimiters );
str
C string to truncate. Notice that this string is modified by being broken into smaller strings (tokens). Alternativelly, a null pointer may be specified, in which case the function continues scanning where a previous successful call to the function ended.
delimiters
C string containing the delimiter characters. These can be different from one call to another. If a token is found, function returns a pointer to the beginning of the token. Otherwise, a null pointer. A null pointer is always returned when the end of the string (i.e., a null character) is reached in the string being scanned. To determine the beginning and the end of a token, the function first scans from the starting location for the first character not contained in delimiters (which becomes the beginning of the token). And then scans starting from this beginning of the token for the first character contained in delimiters, which becomes the end of the token. The scan also stops if the terminating null character is found. This end of the token is automatically replaced by a null-character, and the beginning of the token is returned by the function. Once the terminating null character of str is found in a call to strtok, all subsequent calls to this function (with a null pointer as the first argument) return a null pointer. The point where the last token was found is kept internally by the function to be used on the next call (particular library implementations are not required to avoid data races).
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/* divides a string into tokens by strtok() string function code example */ // program for splitting a string // using strtok() #include <stdio.h> #include <string.h> int main() { char str[] = "HappyCodings"; // Returns first token char* token = strtok(str, "-"); // Keep printing tokens while one of the // delimiters present in str[]. while (token != NULL) { printf("%s\n", token); token = strtok(NULL, "-"); } return 0; }
Logical Operators in C
An expression containing logical operator returns either 0 or 1 depending upon whether expression results true or false. Logical operators are commonly used in decision making in C programming. These operators are used to perform logical operations and used with conditional statements like C if-else statements.
&&
Called Logical AND operator. If both the operands are non-zero, then the condition becomes true.
||
Called Logical OR Operator. If any of the two operands is non-zero, then the condition becomes true.
!
Called Logical NOT Operator. It is used to reverse the logical state of its operand. If a condition is true, then Logical NOT operator will make it false.
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/* logical operators in C language */ #include <stdio.h> main() { int a = 4; int b = 23; int c ; if ( a && b ) { printf("Line 1 - Condition is true\n" ); } if ( a || b ) { printf("Line 2 - Condition is true\n" ); } /* lets change the value of a and b */ a = 2; b = 8; if ( a && b ) { printf("Line 3 - Condition is true\n" ); } else { printf("Line 3 - Condition is not true\n" ); } if ( !(a && b) ) { printf("Line 4 - Condition is true\n" ); } }
freopen() Function in C
Reopen stream with different file or mode. Reuses stream to either open the file specified by filename or to change its access mode. If a new filename is specified, the function first attempts to close any file already associated with stream (third parameter) and disassociates it. Then, independently of whether that stream was successfuly closed or not, freopen opens the file specified by filename and associates it with the stream just as fopen would do using the specified mode. If filename is a null pointer, the function attempts to change the mode of the stream. Although a particular library implementation is allowed to restrict the changes permitted, and under which circumstances. The error indicator and eof indicator are automatically cleared (as if clearerr was called). This function is especially useful for redirecting predefined streams like stdin, stdout and stderr to specific files (see the example below).
Syntax for freopen() Function in C
#include <stdio.h> FILE * freopen ( const char * filename, const char * mode, FILE * stream );
filename
C string containing the name of the file to be opened. Its value shall follow the file name specifications of the running environment and can include a path (if supported by the system). If this parameter is a null pointer, the function attempts to change the mode of the stream, as if the file name currently associated with that stream had been used.
mode
C string containing a file access mode. It can be:
r read
Open file for input operations. The file must exist.
w write
Create an empty file for output operations. If a file with the same name already exists, its contents are discarded and the file is treated as a new empty file.
a append
Open file for output at the end of a file. Output operations always write data at the end of the file, expanding it. Repositioning operations (fseek, fsetpos, rewind) are ignored. The file is created if it does not exist.
r+ read/update
Open a file for update (both for input and output). The file must exist.
w+ write/update
Create an empty file and open it for update (both for input and output). If a file with the same name already exists its contents are discarded and the file is treated as a new empty file.
a+ append/update
Open a file for update (both for input and output) with all output operations writing data at the end of the file. Repositioning operations (fseek, fsetpos, rewind) affects the next input operations, but output operations move the position back to the end of file. The file is created if it does not exist. With the mode specifiers above the file is open as a text file. In order to open a file as a binary file, a "b" character has to be included in the mode string. This additional "b" character can either be appended at the end of the string (thus making the following compound modes: "rb", "wb", "ab", "r+b", "w+b", "a+b") or be inserted between the letter and the "+" sign for the mixed modes ("rb+", "wb+", "ab+"). The new C standard (C2011, which is not part of C++) adds a new standard subspecifier ("x"), that can be appended to any "w" specifier (to form "wx", "wbx", "w+x" or "w+bx"/"wb+x"). This subspecifier forces the function to fail if the file exists, instead of overwriting it. If additional characters follow the sequence, the behavior depends on the library implementation: some implementations may ignore additional characters so that for example an additional "t" (sometimes used to explicitly state a text file) is accepted. On some library implementations, opening or creating a text file with update mode may treat the stream instead as a binary file.
stream
pointer to a FILE object that identifies the stream to be reopened. If the file is successfully reopened, the function returns the pointer passed as parameter stream, which can be used to identify the reopened stream. Otherwise, a null pointer is returned. On most library implementations, the errno variable is also set to a system-specific error code on failure.
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/* reuses stream to either open the file specified by filename or to change its access mode by freopen() function code example */ #include <stdio.h> #include <stdlib.h> int main() { //Initialize the file pointer FILE *f, *fp; //Take a array of characters char ch[100]; //Create the file for write operation f = fopen("myfile.txt", "w"); printf("Enter five strings\n"); for (int i = 0; i < 4; i++) { //take the strings from the users scanf("%[^\n]", &ch); //write back to the file fputs(ch, f); //every time take a new line for the new entry string //except for last entry. Otherwise print the last line twice fputs("\n", f); //clear the stdin stream buffer //if we don't write this then after taking string fflush(stdin); } //%[^\n] is waiting for the '\n' or white space //take the strings from the users scanf("%[^\n]", &ch); fputs(ch, f); //reopen the file for read operation fp = freopen("myfile.txt", "r", fp); printf("File content is--\n"); printf("\n...............print the strings..............\n\n"); while (!feof(fp)) { //takes the first 100 character in the character array fgets(ch, 100, fp); //and print the strings printf("%s", ch); } //close the files fclose(fp); fclose(f); return 0; }
main() Function in C
In C, the "main" function is treated the same as every function, it has a return type (and in some cases accepts inputs via parameters). The only difference is that the main function is "called" by the operating system when the user runs the program. Thus the main function is always the first code executed when a program starts. main() function is a user defined, body of the function is defined by the programmer or we can say main() is programmer/user implemented function, whose prototype is predefined in the compiler. Hence we can say that main() in c programming is user defined as well as predefined because it's prototype is predefined. main() is a system (compiler) declared function whose defined by the user, which is invoked automatically by the operating system when program is being executed. Its first function or entry point of the program from where program start executed, program's execution starts from the main. So main is an important function in c , c++ programming language.
Syntax for main() Function in C
void main() { ......... // codes start from here ......... }
void
is a keyword in C language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value. In place of void we can also use int return type of main() function, at that time main() return integer type value.
main
is a name of function which is predefined function in C library. • An operating system always calls the main() function when a programmers or users execute their programming code. • It is responsible for starting and ends of the program. • It is a universally accepted keyword in programming language and cannot change its meaning and name. • A main() function is a user-defined function in C that means we can pass parameters to the main() function according to the requirement of a program. • A main() function is used to invoke the programming code at the run time, not at the compile time of a program. • A main() function is followed by opening and closing parenthesis brackets.
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/* basic c program by main() function example */ #include <stdio.h> #include <conio.h> main() { printf (" It is a main() function "); int fun2(); // jump to void fun1() function printf ("\n Finally exit from the main() function. "); } void fun1() { printf (" It is a second function. "); printf (" Exit from the void fun1() function. "); } int fun2() { void fun1(); // jump to the int fun1() function printf (" It is a third function. "); printf (" Exit from the int fun2() function. "); return 0; }
#define Directive in C
In the C Programming Language, the #define directive allows the definition of macros within your source code. These macro definitions allow constant values to be declared for use throughout your code. Macro definitions are not variables and cannot be changed by your program code like variables. You generally use this syntax when creating constants that represent numbers, strings or expressions.
Syntax for #define Directive in C
#define NAME value /* this syntax creates a constant using define*/ // Or #define NAME (expression) /* this syntax creates a constant using define*/
NAME
is the name of a particular constant. It can either be defined in smaller case or upper case or both. Most of the developers prefer the constant names to be in the upper case to find the differences.
value
defines the value of the constant.
Expression
is the value that is assigned to that constant which is defined. The expression should always be enclosed within the brackets if it has any operators. In the C programming language, the preprocessor directive acts an important role within which the #define directive is present that is used to define the constant or the micro substitution. The #define directive can use any of the basic data types present in the C standard. The #define preprocessor directive lets a programmer or a developer define the macros within the source code. This macro definition will allow the constant value that should be declared for the usage. Macro definitions cannot be changed within the program's code as one does with other variables, as macros are not variables. The #define is usually used in syntax that created a constant that is used to represent numbers, strings, or other expressions. The #define directive should not be enclosed with the semicolon(;). It is a common mistake done, and one should always treat this directive as any other header file. Enclosing it with a semicolon will generate an error. The #define creates a macro, which is in association with an identifier or is parameterized identifier along with a token string. After the macro is defined, then the compiler can substitute the token string for each occurrence of the identifier within the source file.
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/* #define directive allows the definition of macros within your source code. These macro definitions allow constant values to be declared for use throughout your code. */ #include <stdio.h> #include <string.h> typedef struct Books { char title[50]; char author[50]; char subject[100]; int book_id; } Book; int main( ) { Book book; strcpy( book.title, "C Programming"); strcpy( book.author, "XCoder"); strcpy( book.subject, "C Programming Tutorial"); book.book_id = 6495407; printf( "Book title : %s\n", book.title); printf( "Book author : %s\n", book.author); printf( "Book subject : %s\n", book.subject); printf( "Book book_id : %d\n", book.book_id); return 0; }
exit() Function in C
The exit() function is used to terminate a process or function calling immediately in the program. It means any open file or function belonging to the process is closed immediately as the exit() function occurred in the program. The exit() function is the standard library function of the C, which is defined in the stdlib.h header file. So, we can say it is the function that forcefully terminates the current program and transfers the control to the operating system to exit the program. The exit(0) function determines the program terminates without any error message, and then the exit(1) function determines the program forcefully terminates the execution process.
Syntax for exit() Function in C
#include <stdlib.h> void exit(int status)
status
Status code. If this is 0 or EXIT_SUCCESS, it indicates success. If it is EXIT_FAILURE, it indicates failure. The exit function does not return anything. • We must include the stdlib.h header file while using the exit () function. • It is used to terminate the normal execution of the program while encountered the exit () function. • The exit () function calls the registered atexit() function in the reverse order of their registration. • We can use the exit() function to flush or clean all open stream data like read or write with unwritten buffered data. • It closed all opened files linked with a parent or another function or file and can remove all files created by the tmpfile function. • The program's behaviour is undefined if the user calls the exit function more than one time or calls the exit and quick_exit function. • The exit function is categorized into two parts: exit(0) and exit(1).
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/* call all functions registered with atexit and terminates the program by exit() function example */ #include <stdio.h> #include <stdlib.h> int main () { // declaration of the variables int i, num; printf ( " Enter the last number: "); scanf ( " %d", &num); for ( i = 1; i<num; i++) { // use if statement to check the condition if ( i == 6 ) /* use exit () statement with passing 0 argument to show termination of the program without any error message. */ exit(0); else printf (" \n Number is %d", i); } return 0; }
open() Function in C
The open() function shall establish the connection between a file and a file descriptor. It shall create an open file description that refers to a file and a file descriptor that refers to that open file description. The file descriptor is used by other I/O functions to refer to that file. The path argument points to a pathname naming the file. The open() function shall return a file descriptor for the named file that is the lowest file descriptor not currently open for that process. The open file description is new, and therefore the file descriptor shall not share it with any other process in the system. The FD_CLOEXEC file descriptor flag associated with the new file descriptor shall be cleared.
Syntax for open() Function in C
#include <fcntl.h> int open(const char *path, int oflag, ... );
path
path to file which you want to use
oflag
How you like to use The file offset used to mark the current position within the file shall be set to the beginning of the file. The file status flags and file access modes of the open file description shall be set according to the value of oflag. Values for oflag are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>. Applications shall specify exactly one of the first three values (file access modes) below in the value of oflag:
O_RDONLY
Open for reading only.
O_WRONLY
Open for writing only.
O_RDWR
Open for reading and writing. The result is undefined if this flag is applied to a FIFO. Any combination of the following may be used:
O_APPEND
If set, the file offset shall be set to the end of the file prior to each write.
O_CREAT
If the file exists, this flag has no effect except as noted under O_EXCL below. Otherwise, the file shall be created; the user ID of the file shall be set to the effective user ID of the process; the group ID of the file shall be set to the group ID of the file's parent directory or to the effective group ID of the process; and the access permission bits (see <sys/stat.h>) of the file mode shall be set to the value of the third argument taken as type mode_t modified as follows: a bitwise AND is performed on the file-mode bits and the corresponding bits in the complement of the process' file mode creation mask. Thus, all bits in the file mode whose corresponding bit in the file mode creation mask is set are cleared. When bits other than the file permission bits are set, the effect is unspecified. The third argument does not affect whether the file is open for reading, writing, or for both. Implementations shall provide a way to initialize the file's group ID to the group ID of the parent directory. Implementations may, but need not, provide an implementation-defined way to initialize the file's group ID to the effective group ID of the calling process.
O_DSYNC
Write I/O operations on the file descriptor shall complete as defined by synchronized I/O data integrity completion.
O_EXCL
If O_CREAT and O_EXCL are set, open() shall fail if the file exists. The check for the existence of the file and the creation of the file if it does not exist shall be atomic with respect to other threads executing open() naming the same filename in the same directory with O_EXCL and O_CREAT set. If O_EXCL and O_CREAT are set, and path names a symbolic link, open() shall fail and set errno to [EEXIST], regardless of the contents of the symbolic link. If O_EXCL is set and O_CREAT is not set, the result is undefined.
O_NOCTTY
If set and path identifies a terminal device, open() shall not cause the terminal device to become the controlling terminal for the process.
O_NONBLOCK
When opening a FIFO with O_RDONLY or O_WRONLY set: • If O_NONBLOCK is set, an open() for reading-only shall return without delay. An open() for writing-only shall return an error if no process currently has the file open for reading. • If O_NONBLOCK is clear, an open() for reading-only shall block the calling thread until a thread opens the file for writing. An open() for writing-only shall block the calling thread until a thread opens the file for reading. When opening a block special or character special file that supports non-blocking opens: • If O_NONBLOCK is set, the open() function shall return without blocking for the device to be ready or available. Subsequent behavior of the device is device-specific. • If O_NONBLOCK is clear, the open() function shall block the calling thread until the device is ready or available before returning. Otherwise, the behavior of O_NONBLOCK is unspecified.
O_RSYNC
Read I/O operations on the file descriptor shall complete at the same level of integrity as specified by the O_DSYNC and O_SYNC flags. If both O_DSYNC and O_RSYNC are set in oflag, all I/O operations on the file descriptor shall complete as defined by synchronized I/O data integrity completion. If both O_SYNC and O_RSYNC are set in flags, all I/O operations on the file descriptor shall complete as defined by synchronized I/O file integrity completion.
O_SYNC
Write I/O operations on the file descriptor shall complete as defined by synchronized I/O file integrity completion.
O_TRUNC
If the file exists and is a regular file, and the file is successfully opened O_RDWR or O_WRONLY, its length shall be truncated to 0, and the mode and owner shall be unchanged. It shall have no effect on FIFO special files or terminal device files. Its effect on other file types is implementation-defined. The result of using O_TRUNC with O_RDONLY is undefined. If O_CREAT is set and the file did not previously exist, upon successful completion, open() shall mark for update the st_atime, st_ctime, and st_mtime fields of the file and the st_ctime and st_mtime fields of the parent directory. If O_TRUNC is set and the file did previously exist, upon successful completion, open() shall mark for update the st_ctime and st_mtime fields of the file. If both the O_SYNC and O_DSYNC flags are set, the effect is as if only the O_SYNC flag was set. If path refers to a STREAMS file, oflag may be constructed from O_NONBLOCK OR'ed with either O_RDONLY, O_WRONLY, or O_RDWR. Other flag values are not applicable to STREAMS devices and shall have no effect on them. The value O_NONBLOCK affects the operation of STREAMS drivers and certain functions applied to file descriptors associated with STREAMS files. For STREAMS drivers, the implementation of O_NONBLOCK is device-specific. If path names the master side of a pseudo-terminal device, then it is unspecified whether open() locks the slave side so that it cannot be opened. Conforming applications shall call unlockpt() before opening the slave side. The largest value that can be represented correctly in an object of type off_t shall be established as the offset maximum in the open file description. Upon successful completion, the function shall open the file and return a non-negative integer representing the lowest numbered unused file descriptor. Otherwise, -1 shall be returned and errno set to indicate the error. No files shall be created or modified if the function returns -1. The open() function shall fail if:
EACCES
Search permission is denied on a component of the path prefix, or the file exists and the permissions specified by oflag are denied, or the file does not exist and write permission is denied for the parent directory of the file to be created, or O_TRUNC is specified and write permission is denied.
EEXIST
O_CREAT and O_EXCL are set, and the named file exists.
EINTR
A signal was caught during open().
EINVAL
The implementation does not support synchronized I/O for this file.
EIO
The path argument names a STREAMS file and a hangup or error occurred during the open().
EISDIR
The named file is a directory and oflag includes O_WRONLY or O_RDWR.
ELOOP
A loop exists in symbolic links encountered during resolution of the path argument.
EMFILE
{OPEN_MAX} file descriptors are currently open in the calling process.
ENAMETOOLONG
The length of the path argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
ENFILE
The maximum allowable number of files is currently open in the system.
ENOENT
O_CREAT is not set and the named file does not exist; or O_CREAT is set and either the path prefix does not exist or the path argument points to an empty string.
ENOSR
The path argument names a STREAMS-based file and the system is unable to allocate a STREAM.
ENOSPC
The directory or file system that would contain the new file cannot be expanded, the file does not exist, and O_CREAT is specified.
ENOTDIR
A component of the path prefix is not a directory.
ENXIO
O_NONBLOCK is set, the named file is a FIFO, O_WRONLY is set, and no process has the file open for reading.
ENXIO
The named file is a character special or block special file, and the device associated with this special file does not exist.
EOVERFLOW
The named file is a regular file and the size of the file cannot be represented correctly in an object of type off_t.
EROFS
The named file resides on a read-only file system and either O_WRONLY, O_RDWR, O_CREAT (if the file does not exist), or O_TRUNC is set in the oflag argument. The open() function may fail if:
EAGAIN
The path argument names the slave side of a pseudo-terminal device that is locked.
EINVAL
The value of the oflag argument is not valid.
ELOOP
More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.
ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the path argument, the length of the substituted pathname string exceeded {PATH_MAX}.
ENOMEM
The path argument names a STREAMS file and the system is unable to allocate resources.
ETXTBSY
The file is a pure procedure (shared text) file that is being executed and oflag is O_WRONLY or O_RDWR.
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/* open or create a file for reading, writing or executing by open() function code example */ // C program to illustrate // open system call #include<stdio.h> #include<fcntl.h> #include<errno.h> extern int errno; int main() { // if file does not have in directory // then file foo.txt is created. int fd = open("foo.txt", O_RDONLY | O_CREAT); printf("fd = %d/n", fd); if (fd ==-1) { // print which type of error have in a code printf("Error Number % d\n", errno); // print program detail "Success or failure" perror("Program"); } return 0; }
perror() Function in C
Print error message. Interprets the value of errno as an error message, and prints it to stderr (the standard error output stream, usually the console), optionally preceding it with the custom message specified in str. errno is an integral variable whose value describes the error condition or diagnostic information produced by a call to a library function (any function of the C standard library may set a value for errno, even if not explicitly specified in this reference, and even if no error happened), see errno for more info.
Syntax for perror() Function in C
#include <stdio.h> void perror ( const char * str );
str
C string containing a custom message to be printed before the error message itself. If it is a null pointer, no preceding custom message is printed, but the error message is still printed. By convention, the name of the application itself is generally used as parameter. This function does not return any value. The error message produced by perror is platform-depend. If the parameter str is not a null pointer, str is printed followed by a colon (:) and a space. Then, whether str was a null pointer or not, the generated error description is printed followed by a newline character ('\n'). perror should be called right after the error was produced, otherwise it can be overwritten by calls to other functions.
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/* print an error message corresponding to the value of errno with perror() function code example */ /* error handling with perror() function and errno */ #include <stdio.h> #include <stdlib.h> #include <errno.h> main() { FILE *fp; char filename[80]; printf("Enter filename: "); gets(filename); if (( fp = fopen(filename, "r")) == NULL) { perror("You goofed!"); printf("errno = %d.\n", errno); exit(1); } else { puts("File opened for reading."); fclose(fp); } return(0); }
strlen() Function in C
Get string length. Returns the length of the C string str. The length of a C string is determined by the terminating null-character: A C string is as long as the number of characters between the beginning of the string and the terminating null character (without including the terminating null character itself).
Syntax for strlen() Function in C
#include <string.h> size_t strlen ( const char * str );
str
C string Function returns the length of string. This should not be confused with the size of the array that holds the string. strlen() function is defined in string.h header file. It doesn't count null character '\0'.
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/* get the length of the C string str by strlen() function example */ /* Program to find the total length of a String using strlen() */ #include<stdio.h> #include<string.h> int main() { char str1[10]= "01234567"; /* First string */ printf("First String is %s",str1); printf("\n"); int length = strlen(str1); printf("Length of first String is %d", length); printf("\n"); char str2[20]= "String Chapter"; /* Second string */ printf("Second String is %s",str2); printf("\n"); length = strlen(str2); printf("Length of second String is %d", length); return 0; }
isalpha() Function in C
Check if character is alphabetic. Checks whether c is an alphabetic letter. Notice that what is considered a letter depends on the locale being used; In the default "C" locale, what constitutes a letter is only what returns true by either isupper or islower. Using other locales, an alphabetic character is a character for which isupper or islower would return true, or another character explicitly considered alphabetic by the locale (in this case, the character cannot be iscntrl, isdigit, ispunct or isspace). For a detailed chart on what the different ctype functions return for each character of the standard ANSII character set, see the reference for the <cctype> header. In C++, a locale-specific template version of this function (isalpha) exists in header <locale>.
Syntax for isalpha() Function in C
#include <ctype.h> int isalpha ( int c );
c
Character to be checked, casted to an int, or EOF. Function returns a value different from zero (i.e., true) if indeed c is an alphabetic letter. Zero (i.e., false) otherwise. isalpha(c) is a function in C which can be used to check if the passed character is an alphabet or not. It returns a non-zero value if it's an alphabet else it returns 0. It returns non-zero values for 'a' to 'z' and 'A' to 'Z' and zeroes for other characters. We should include ctype.h header to use isalpha() function.
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/* check if character is alphabetic by isalpha() function example */ #include <stdio.h> #include <ctype.h> int main () { int var1 = 'd'; int var2 = '2'; int var3 = '\t'; int var4 = ' '; if( isalpha(var1) ) { printf("var1 = |%c| is an alphabet\n", var1 ); } else { printf("var1 = |%c| is not an alphabet\n", var1 ); } if( isalpha(var2) ) { printf("var2 = |%c| is an alphabet\n", var2 ); } else { printf("var2 = |%c| is not an alphabet\n", var2 ); } if( isalpha(var3) ) { printf("var3 = |%c| is an alphabet\n", var3 ); } else { printf("var3 = |%c| is not an alphabet\n", var3 ); } if( isalpha(var4) ) { printf("var4 = |%c| is an alphabet\n", var4 ); } else { printf("var4 = |%c| is not an alphabet\n", var4 ); } return(0); }
setlocale() Function in C
Set or retrieve locale. Sets locale information to be used by the current program, either changing the entire locale or portions of it. The function can also be used to retrieve the current locale's name by passing NULL as the value for argument locale. Locales contain information on how to interpret and perform certain input/output and transformation operations taking into consideration location and language specific settings. Most running environments have certain locale information set according to the user preferences or localization. But, independently of this system locale, on start, all C programs have the "C" locale set, which is a rather neutral locale with minimal locale information that allows the result of programs to be predictable. In order to use the default locale set in the environment, this function can be called with "" as argument locale. On program startup, the locale selected is the "C" locale, which is the same as would be set by calling setlocale(LC_ALL,"C"). The locale settings selected in the environment can be selected by calling setlocale(LC_ALL,""). The portions of the current locale affected by a call to this function are specified by argument category.
Syntax for setlocale() Function in C
#include <locale.h> char* setlocale (int category, const char* locale);
category
Portion of the locale affected. It is one of the following constant values defined as macros in :
LC_ALL
Selects all the C locale
LC_COLLATE
Selection the collation category
LC_CTYPE
Selects the character classification category
LC_MONETARY
Selects the monetary formatting category
LC_NUMERIC
Selects the numeric formatting category
LC_TIME
Selects the time formatting category
LC_MESSAGES
specify the language to be used for messages.
locale
C string containing the name of a C locale. These are system specific, but at least the two following locales must exist:
"C"
Minimal "C" locale
""
Environment's default locale If the value of this parameter is NULL, the function does not make any changes to the current locale, but the name of the current locale is still returned by the function. On success, function returns a pointer to a C string identifying the locale currently set for the category. If category is LC_ALL and different portions of the locale are set to different values, the string returned gives this information in a format which may vary between library implementations. If the function failed to set a new locale, this is not modified and a null pointer is returned.
Data races
Changing locale settings may introduce data races with concurrent calls to the same function or to any C-library function affected by the locale.
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/* set or retrieve locale by setlocale() function code example */ #include <stdio.h> #include <locale.h> int main(int argc, const char * argv[]) { /* Define a temporary variable */ struct lconv *loc; /* Set the locale to the POSIX C environment */ setlocale (LC_ALL, "C"); /* Retrieve a pointer to the current locale */ loc = localeconv(); /* Display some of the locale settings */ printf("Thousands Separator: %s\n", loc->thousands_sep); printf("Currency Symbol: %s\n", loc->currency_symbol); /* Set the locale to the environment default */ setlocale (LC_ALL, ""); /* Retrieve a pointer to the current locale */ loc = localeconv(); /* Display some of the locale settings */ printf("Thousands Separator: %s\n", loc->thousands_sep); printf("Currency Symbol: %s\n", loc->currency_symbol); return 0; }
While Loop Statement in C
While loop is also known as a pre-tested loop. In general, a while loop allows a part of the code to be executed multiple times depending upon a given boolean condition. It can be viewed as a repeating if statement. The while loop is mostly used in the case where the number of iterations is not known in advance. The while loop evaluates the test expression inside the parentheses (). If test expression is true, statements inside the body of while loop are executed. Then, test expression is evaluated again. The process goes on until test expression is evaluated to false. If test expression is false, the loop terminates.
Syntax of While Loop Statement in C
while (testExpression) { // the body of the loop }
• The while loop evaluates the testExpression inside the parentheses (). • If testExpression is true, statements inside the body of while loop are executed. Then, testExpression is evaluated again. • The process goes on until testExpression is evaluated to false. • If testExpression is false, the loop terminates (ends).
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/* while loop statement in C language */ #include<stdio.h> int main() { int n, num, sum = 0, remainder; printf("Enter a number: "); scanf("%d", &n); num = n; // keep looping while n > 0 while( n > 0 ) { remainder = n % 10; // get the last digit of n sum += remainder; // add the remainder to the sum n /= 10; // remove the last digit from n } printf("Sum of digits of %d is %d", num, sum); // signal to operating system everything works fine return 0; }
close() Function in C
Closes a file descriptor, fildes. This frees the file descriptor to be returned by future open() calls and other calls that create file descriptors. The fildes argument must represent a hierarchical file system (HFS) file. When the last open file descriptor for a file is closed, the file itself is closed. If the file's link count is 0 at that time, its space is freed and the file becomes inaccessible. When the last open file descriptor for a pipe or FIFO file is closed, any data remaining in the pipe or FIFO file is discarded. close() unlocks (removes) all outstanding record locks that a process has on the associated file.
Syntax for close() Function in C
#include <unistd.h> int close(int fildes);
fildes
The descriptor of the socket to be closed. Behavior for sockets: close() call shuts down the socket associated with the socket descriptor socket, and frees resources allocated to the socket. If socket refers to an open TCP connection, the connection is closed. If a stream socket is closed when there is input data queued, the TCP connection is reset rather than being cleanly closed. All sockets should be closed before the end of your process. You should issue a shutdown() call before you issue a close() call for a socket. For AF_INET and AF_INET6 stream sockets (SOCK_STREAM) using SO_LINGER socket option, the socket does not immediately end if data is still present when a close is issued. The following structure is used to set or unset this option, and it can be found in sys/socket.h.
struct linger { int l_onoff; /* zero=off, nonzero=on */ int l_linger; /* time is seconds to linger */ };
If the l_onoff switch is nonzero, the system attempts to deliver any unsent messages. If a linger time is specified, the system waits for n seconds before flushing the data and terminating the socket. For AF_UNIX, when closing sockets that were bound, you should also use unlink() to delete the file created at bind() time. Special behavior for XPG4.2: If a STREAMS-based fildes is closed and the calling process was previously registered to receive a SIGPOLL signal for events associated with that STREAM, the calling process will be unregistered for events associated with the STREAM. The last close() for a STREAM causes the STREAM associated with fildes to be dismantled. If O_NONBLOCK is not set and there have been no signals posted for the STREAM, and if there is data on the module's write queue, close() waits for an unspecified time (for each module and driver) for any output to drain before dismantling the STREAM. The time delay can be changed using an I_SETCLTIME ioctl() request. If the O_NONBLOCK flag is set, or if there are any pending signals, close() does not wait for output to drain, and dismantles the STREAM immediately. Note: z/OS® UNIX services do not supply any STREAMS devices or pseudodevices. See open() - Open a file for more information. If fildes refers to the master side of a pseudoterminal, a SIGHUP signal is sent to the process group, if any, for which the slave side of the pseudoterminal is the controlling terminal. If fildes refers to the slave side of a pseudoterminal, a zero-length message will be sent to the master. If fildes refers to a socket, close() causes the socket to be destroyed. If the socket is connection-oriented and the SO_LINGER option is set for the socket and the socket has untransmitted data, then close() will block for up to the current linger interval until all data is transmitted. If successful, close() returns 0. If unsuccessful, close() returns -1 and sets errno to one of the following values:
EAGAIN
The call did not complete because the specified socket descriptor is currently being used by another thread in the same process. For example, in a multithreaded environment, close() fails and returns EAGAIN when the following sequence of events occurs (1) thread is blocked in a read() or select() call on a given file or socket descriptor and (2) another thread issues a simultaneous close() call for the same descriptor.
EBADF
fildes is not a valid open file descriptor, or the socket parameter is not a valid socket descriptor.
EBUSY
The file cannot be closed because it is blocked.
EINTR
close() was interrupted by a signal. The file may or may not be closed.
EIO
Added for XPG4.2: An I/O error occurred while reading from or writing to the file system.
ENXIO
fildes does not exist. The minor number for the file is incorrect.
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/* close a file descriptor by close() function code example */ #include <fcntl.h> #include <unistd.h> #include <stdlib.h> int main( void ) { int filedes; filedes = open( "file", O_RDONLY ); if( filedes != -1 ) { /* process file */ close( filedes ); return EXIT_SUCCESS; } return EXIT_FAILURE; }
For Loop Statement in C
The for loop is used in the case where we need to execute some part of the code until the given condition is satisfied. The for loop is also called as a per-tested loop. It is better to use for loop if the number of iteration is known in advance. The for-loop statement is a very specialized while loop, which increases the readability of a program. It is frequently used to traverse the data structures like the array and linked list.
Syntax of For Loop Statement in C
for (initialization; condition test; increment or decrement) { //Statements to be executed repeatedly }
Step 1
First initialization happens and the counter variable gets initialized.
Step 2
In the second step the condition is checked, where the counter variable is tested for the given condition, if the condition returns true then the C statements inside the body of for loop gets executed, if the condition returns false then the for loop gets terminated and the control comes out of the loop.
Step 3
After successful execution of statements inside the body of loop, the counter variable is incremented or decremented, depending on the operation (++ or --).
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/* for loop statement in C language */ // Program to calculate the sum of first n natural numbers // Positive integers 1,2,3...n are known as natural numbers #include <stdio.h> int main() { int num, count, sum = 0; printf("Enter a positive integer: "); scanf("%d", &num); // for loop terminates when num is less than count for(count = 1; count <= num; ++count) { sum += count; } printf("Sum = %d", sum); return 0; }
Break Statement in C
The break is a keyword in C which is used to bring the program control out of the loop. The break statement is used inside loops or switch statement. The break statement breaks the loop one by one, i.e., in the case of nested loops, it breaks the inner loop first and then proceeds to outer loops.
Syntax for Break Statement in C
//loop statement... break;
When a break statement is encountered inside a loop, the loop is immediately terminated and the program control resumes at the next statement following the loop. It can be used to terminate a case in the switch statement (covered in the next chapter). If you are using nested loops, the break statement will stop the execution of the innermost loop and start executing the next line of code after the block.
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/* bring the program control out of the loop by break keyword */ // Program to calculate the sum of numbers (10 numbers max) // If the user enters a negative number, the loop terminates #include <stdio.h> int main() { int i; double number, sum = 0.0; for (i = 1; i <= 10; ++i) { printf("Enter n%d: ", i); scanf("%lf", &number); // if the user enters a negative number, break the loop if (number < 0.0) { break; } sum += number; // sum = sum + number; } printf("Sum = %.2lf", sum); return 0; }
regcomp() Function in C
A regular expression is a sequence of characters used to match a pattern to a string. The expression can be used for searching text and validating input. Remember, a regular expression is not the property of a particular language. POSIX is a well-known library used for regular expressions in C. Patterns in the POSIX library: [] - Used to find any of the characters or numbers specified between the brackets. [:number:] - Used to find any digit. [:lower:] - Used to find lowercase alphabets. [:word:] - Used to find letters numbers and underscores. Compiles the regular expression specified by pattern into an executable string of op-codes.
Syntax for regcomp() Function in C
#include <regex.h> int regcomp(regex_t *_restrict_ preg, const char *_restrict_ pattern, int cflags);
preg
preg is a pointer to a compiled regular expression.
pattern
pattern is a pointer to a character string defining a source regular expression (described below).
cflags
cflags is a bit flag defining configurable attributes of compilation process:
REG_EXTENDED
Support extended regular expressions.
REG_ICASE
Ignore case in match.
REG_NEWLINE
Eliminate any special significance to the newline character.
REG_NOSUB
Report only success or fail in regexec(), that is, verify the syntax of a regular expression. If this flag is set, the regcomp() function sets re_nsub to the number of parenthesized sub-expressions found in pattern. Otherwise, a sub-expression results in an error. If successful, regcomp() returns 0. If unsuccessful, regcomp() returns nonzero, and the content of preg is undefined. The regcomp() function under z/OS XL C/C++ will use the definition of characters according to the current LC_SYNTAX category. The characters, [, ], {, }, |, ^, and $, have varying code points in different encoded character sets. The functions regcomp(), regerror(), regexec(), and regfree() use regular expressions in a similar way to the UNIX awk, ed, grep, and egrep commands. The simplest form of regular expression is a string of characters with no special meaning. The following characters do have special meaning; they are used to form extended regular expressions: . The period symbol matches any one character except the terminal newline character. [character-character] The hyphen symbol, within square brackets, means "through". It fills in the intervening characters according to the current collating sequence. For example, [a-z] can be equivalent to [abc...xyz] or, with a different collating sequence, it can be equivalent to [aAbBcC...xXyYzZ]. [string] A string within square brackets specifies any of the characters in string. Thus [abc], if compared to other strings, would match any that contained a, b, or c. No assumptions are made at compile time about the actual characters contained in the range. {m} {m,} {m,u} Integer values enclosed in {} indicate the number of times to apply the preceding regular expression. m is the minimum number, and u is the maximum number. u must not be greater than RE_DUP_MAX (see limits.h). If you specify only m, it indicates the exact number of times to apply the regular expression. {m,} is equivalent to {m,u}. They both match m or more occurrences of the expression. * The asterisk symbol indicates 0 or more of any characters. For example, [a*e] is equivalent to any of the following: 99ae9, aaaaae, a999e99. $ The dollar symbol matches the end of the string. (Use \n to match a newline character.) character+ The plus symbol specifies one or more occurrences of a character. Thus, smith+ern is equivalent to, for example, smithhhern. [^string] The caret symbol, when inside square brackets, negates the characters within the square brackets. Thus [^abc], if compared to other strings, would fail to match any that contains even one a, b, or c. (expression)$n Stores the value matched by the enclosed regular expression in the (n+1)th ret parameter. Ten enclosed regular expressions are allowed. Assignments are made unconditionally. (expression) Groups a sub-expression allowing an operator, such as *, +, or [].], to work on the sub-expression enclosed in parentheses. For example, (a*(cb+)*)$0. • Do not use multibyte characters. • You can use the ] (right square bracket) alone within a pair of square brackets, but only if it immediately follows either the opening left square bracket or if it immediately follows [^. For example: []-] matches the ] and - characters. • All the preceding symbols are special. You precede them with \ to use the symbol itself. For example, a\.e is equivalent to a.e. • You can use the - (hyphen) by itself, but only if it is the first or last character in the expression. For example, the expression []--0] matches either the ] or else the characters - through 0. Otherwise, use \-.
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/* compile regular expression by regcomp() function code example */ #include <regex.h> /* * Match string against the extended regular expression in * pattern, treating errors as no match. * * Return 1 for match, 0 for no match. */ int match(const char *string, char *pattern) { int status; regex_t re; if (regcomp(&re, pattern, REG_EXTENDED|REG_NOSUB) != 0) { return(0); /* Report error. */ } status = regexec(&re, string, (size_t) 0, NULL, 0); regfree(&re); if (status != 0) { return(0); /* Report error. */ } return(1); }
isdigit() Function in C
Check if character is decimal digit. Checks whether c is a decimal digit character. This function accepts a character and classifies the character as a digit. It returns a value other than 0 to indicate success. The isdigit() function checks if the character is a numeric character. Although isdigit() accepts an integer as an argument, when a character is passed to the function it internally converts the character to an ASCII value. For a detailed chart on what the different ctype functions return for each character of the standard ASCII character set, see the reference for the <cctype> header. Decimal digits are any of: 0 1 2 3 4 5 6 7 8 9
Syntax for isdigit() Function in C
#include <ctype.h> int isdigit ( int c );
c
Character to be checked, casted to an int, or EOF. Function returns a value different from zero (i.e., true) if indeed c is a decimal digit. Zero (i.e., false) otherwise. It takes a single argument in the form of an integer and returns the value of type int. Even though isdigit() takes an integer as an argument, the character is passed to the function. Internally, the character is converted to its ASCII value for the check.
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/* check if character is decimal digit by isdigit() function code example */ #include <stdio.h> #include <ctype.h> int main(int argc, const char * argv[]) { /* Define a temporary variable */ unsigned char test; /* Assign a test decimal digit character to the variable */ test = '7'; /* Test to see if this is a decimal digit character */ if (isdigit(test) != 0) printf("%c is a decimal digit character\n", test); else printf("%c is not a decimal digit character\n", test); /* Assign a non-digit character to the variable */ test = 'T'; /* Test to see if this is a decimal digit character */ if (isdigit(test) != 0) printf("%c is a decimal digit character\n", test); else printf("%c is not a decimal digit character\n", test); return 0; }
#include Directive in C
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program. Here are the two types of file that can be included using #include: • Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. • User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor.
Syntax for #include Directive in C
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories.
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/* #include directive tells the preprocessor to insert the contents of another file into the source code at the point where the #include directive is found. */ // C program to illustrate file inclusion // <> used to import system header file #include <stdio.h> // " " used to import user-defined file #include "process.h" // main function int main() { // add function defined in process.h add(10, 20); // mult function defined in process.h multiply(10, 20); // printf defined in stdio.h printf("Process completed"); return 0; }
fclose() Function in C
Close file. Closes the file associated with the stream and disassociates it. All internal buffers associated with the stream are disassociated from it and flushed: the content of any unwritten output buffer is written and the content of any unread input buffer is discarded. Even if the call fails, the stream passed as parameter will no longer be associated with the file nor its buffers.
Syntax for fclose() Function in C
#include <stdio.h> int fclose ( FILE * stream );
stream
Pointer to a FILE object that specifies the stream to be closed. The fclose() function shall cause the stream pointed to by stream to be flushed and the associated file to be closed. Any unwritten buffered data for the stream shall be written to the file; any unread buffered data shall be discarded. Whether or not the call succeeds, the stream shall be disassociated from the file and any buffer set by the setbuf() or setvbuf() function shall be disassociated from the stream. If the associated buffer was automatically allocated, it shall be deallocated. After the call to fclose(), any use of stream results in undefined behavior. If the stream is successfully closed, a zero value is returned. On failure, EOF is returned.
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/* close the file associated with the stream and disassociates it by close() function example */ /* Open, write and close a file : */ # include <stdio.h> # include <string.h> int main( ) { FILE *fp ; char data[50]; // opening an existing file printf( "Opening the file test.c in write mode" ) ; fp = fopen("test.c", "w") ; if ( fp == NULL ) { printf( "Could not open file test.c" ) ; return 1; } printf( "\n Enter some text from keyboard" \ " to write in the file test.c" ) ; // getting input from user while ( strlen ( gets( data ) ) > 0 ) { // writing in the file fputs(data, fp) ; fputs("\n", fp) ; } // closing the file printf("Closing the file test.c") ; fclose(fp) ; return 0; }
getopt() Function in C
The getopt() function is a builtin function in C and is used to parse command line arguments. The getopt() function is a command-line parser that shall follow Utility Syntax Guidelines 3, 4, 5, 6, 7, 9, and 10 in the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines. The parameters argc and argv are the argument count and argument array as passed to main() (see exec() ). The argument optstring is a string of recognized option characters; if a character is followed by a colon, the option takes an argument. All option characters allowed by Utility Syntax Guideline 3 are allowed in optstring. The implementation may accept other characters as an extension.
Syntax for getopt() Function in C
#include <unistd.h> int getopt(int argc, char * const argv[], const char *optstring); extern char *optarg; extern int optind, opterr, optopt;
argc
The argument count that was passed to main().
argv
The argument array that was passed to main().
optstring
A string of recognized option letters; if a letter is followed by a colon, the option takes an argument. Valid option characters for optstring consist of a single alphanumeric character (i.e. a letter or digit). The variable optind is the index of the next element of the argv[] vector to be processed. It shall be initialized to 1 by the system, and getopt() shall update it when it finishes with each element of argv[]. When an element of argv[] contains multiple option characters, it is unspecified how getopt() determines which options have already been processed. The getopt() function shall return the next option character (if one is found) from argv that matches a character in optstring, if there is one that matches. If the option takes an argument, getopt() shall set the variable optarg to point to the option-argument as follows: 1- If the option was the last character in the string pointed to by an element of argv, then optarg shall contain the next element of argv, and optind shall be incremented by 2. If the resulting value of optind is greater than argc, this indicates a missing option-argument, and getopt() shall return an error indication. 2- Otherwise, optarg shall point to the string following the option character in that element of argv, and optind shall be incremented by 1. If, when getopt() is called:
argv[optind] is a null pointer *argv[optind] is not the character - argv[optind] points to the string "-"
getopt() shall return -1 without changing optind. If:
argv[optind] points to the string "--"
getopt() shall return -1 after incrementing optind. If getopt() encounters an option character that is not contained in optstring, it shall return the question-mark ( '?' ) character. If it detects a missing option-argument, it shall return the colon character ( ':' ) if the first character of optstring was a colon, or a question-mark character ( '?' ) otherwise. In either case, getopt() shall set the variable optopt to the option character that caused the error. If the application has not set the variable opterr to 0 and the first character of optstring is not a colon, getopt() shall also print a diagnostic message to stderr in the format specified for the getopts utility. The getopt() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe. The getopt() function shall return the next option character specified on the command line. A colon ( ':' ) shall be returned if getopt() detects a missing argument and the first character of optstring was a colon ( ':' ). A question mark ( '?' ) shall be returned if getopt() encounters an option character not in optstring or detects a missing argument and the first character of optstring was not a colon ( ':' ). Otherwise, getopt() shall return -1 when all command line options are parsed.
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/* parse command line arguments by getopt() function code example */ // Program to illustrate the getopt() // function in C #include <stdio.h> #include <unistd.h> int main(int argc, char *argv[]) { int opt; // put ':' in the starting of the // string so that program can //distinguish between '?' and ':' while((opt = getopt(argc, argv, ":if:lrx")) != -1) { switch(opt) { case 'i': case 'l': case 'r': printf("option: %c\n", opt); break; case 'f': printf("filename: %s\n", optarg); break; case ':': printf("option needs a value\n"); break; case '?': printf("unknown option: %c\n", optopt); break; } } // optind is for the extra arguments // which are not parsed for(; optind < argc; optind++){ printf("extra arguments: %s\n", argv[optind]); } return 0; }
Nested Loop Statement in C
C supports nesting of loops in C. Nesting of loops is the feature in C that allows the looping of statements inside another loop. Any number of loops can be defined inside another loop, i.e., there is no restriction for defining any number of loops. The nesting level can be defined at n times. You can define any type of loop inside another loop; for example, you can define 'while' loop inside a 'for' loop. A loop inside another loop is called a nested loop. The depth of nested loop depends on the complexity of a problem. We can have any number of nested loops as required. Consider a nested loop where the outer loop runs n times and consists of another loop inside it. The inner loop runs m times. Then, the total number of times the inner loop runs during the program execution is n*m.
Syntax for Nested Loop Statement in C
Outer_loop { Inner_loop { // inner loop statements. } // outer loop statements. }
Outer_loop and Inner_loop are the valid loops that can be a 'for' loop, 'while' loop or 'do-while' loop.
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/* nested loop statement in C language */ // C Program to print all prime factors // of a number using nested loop #include <math.h> #include <stdio.h> // A function to print all prime factors of a given number n void primeFactors(int n) { // Print the number of 2s that divide n while (n % 2 == 0) { printf("%d ", 2); n = n / 2; } // n must be odd at this point. So we can skip // one element (Note i = i +2) for (int i = 3; i <= sqrt(n); i = i + 2) { // While i divides n, print i and divide n while (n % i == 0) { printf("%d ", i); n = n / i; } } // This condition is to handle the case when n // is a prime number greater than 2 if (n > 2) printf("%d ", n); } /* Driver program to test above function */ int main() { int n = 315; primeFactors(n); return 0; }
Continue Statement in C
The continue statement in C programming works somewhat like the break statement. Instead of forcing termination, it forces the next iteration of the loop to take place, skipping any code in between. For the for loop, continue statement causes the conditional test and increment portions of the loop to execute. For the while and do...while loops, continue statement causes the program control to pass to the conditional tests.
Syntax for Continue Statement in C
//loop statements continue; //some lines of the code which is to be skipped
The continue statement in C language is used to bring the program control to the beginning of the loop. The continue statement skips some lines of code inside the loop and continues with the next iteration. It is mainly used for a condition so that we can skip some code for a particular condition.
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/* The continue statement skips the current iteration of the loop and continues with the next iteration. */ // Program to calculate the sum of numbers (10 numbers max) // If the user enters a negative number, it's not added to the result #include <stdio.h> int main() { int i; double number, sum = 0.0; for (i = 1; i <= 10; ++i) { printf("Enter a n%d: ", i); scanf("%lf", &number); if (number < 0.0) { continue; } sum += number; // sum = sum + number; } printf("Sum = %.2lf", sum); return 0; }
fgets() Function in C
Get string from stream. Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a newline or the end-of-file is reached, whichever happens first. A newline character makes fgets stop reading, but it is considered a valid character by the function and included in the string copied to str. A terminating null character is automatically appended after the characters copied to str. Notice that fgets is quite different from gets: not only fgets accepts a stream argument, but also allows to specify the maximum size of str and includes in the string any ending newline character.
Syntax for fgets() Function in C
#include <stdio.h> char * fgets ( char * str, int num, FILE * stream );
str
Pointer to an array of chars where the string read is copied.
num
Maximum number of characters to be copied into str (including the terminating null-character).
stream
Pointer to a FILE object that identifies an input stream. stdin can be used as argument to read from the standard input. On success, the function returns str. If the end-of-file is encountered while attempting to read a character, the eof indicator is set (feof). If this happens before any characters could be read, the pointer returned is a null pointer (and the contents of str remain unchanged). If a read error occurs, the error indicator (ferror) is set and a null pointer is also returned (but the contents pointed by str may have changed).
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/* get string from stream by fgets() function example */ #include<stdio.h> #include<stdlib.h> int main() { char str[50]; FILE *fp; fp = fopen("myfile2.txt", "r"); if(fp == NULL) { printf("Error opening file\n"); exit(1); } printf("Testing fgets() function: \n\n"); printf("Reading contents of myfile.txt: \n\n"); while( fgets(str, 30, fp) != NULL ) { puts(str); } fclose(fp); return 0; }
regexec() Function in C
This is function is used for matching the string with the given pattern of the string. This also has 5 arguments like precompiled pattern, the second parameter which will take string which needs to be searched for, the third parameter contains the details of the location of matches, the fourth parameter contains details of searches, and the fifth parameter contains the flag which gives the indication the change in the matching behavior. This regexec() function returns 0 if there is successful matching done and REG_NOMATCH if the string does not match. Compares the NULL-terminated string specified by string against the compiled regular expression, preg.
Syntax for regexec() Function in C
#include <regex.h> int regexec(const regex_t *preg, const char *string, size_t nmatch, regmatch_t *pmatch, int eflags);
preg
preg is a pointer to a compiled regular expression to compare against STRING.
string
string is a pointer to a string to be matched.
nmatch
nmatch is the number of sub-expressions to match.
pmatch
pmatch is an array of offsets into STRING which matched the corresponding sub-expressions in preg.
eflags
eflags is a bit flag defining customizable behavior of regexec(). If a match is found, regexec() returns 0. If unsuccessful, regexec() returns nonzero indicating either no match or an error. REG_NOTBOL Indicates that the first character of STRING is not the beginning of the line. REG_NOTEOL Indicates that the first character of STRING is not the end of the line. If nmatch parameter is 0 or REG_NOSUB was set on the call to regcomp(), regexec() ignores the pmatch argument. Otherwise, the pmatch argument points to an array of at least nmatch elements. The regexec() function fills in the elements of the array with offsets of the substrings of STRING that correspond to the parenthesized sub-expressions of the original pmatch specified to regcomp(). The 0th element of the array corresponds to the entire pattern. If there are more than nmatch sub-expressions, only the first nmatch-1 are recorded. When matching a basic or extended regular expression, any given parenthesized sub-expression of pmatch might participate in the match of several different substrings of STRING. The following rules determine which substrings are reported in pmatch. • If a sub-expression participated in a match several times, the offset of the last matching substring is reported in pmatch. • If a sub-expression did not match in the source STRING, the offset shown in pmatch is set to -1. • If a sub-expression contains sub-expressions, the data in pmatch refers to the last such sub-expression. • If a sub-expression matches a zero-length string, the offsets in pmatch refer to the byte immediately following the matching string. If EREG_NOSUB was set when regcomp() was called, the contents of pmatch are unspecified. If REG_NEWLINE was set when regcomp() was called, newline characters are allowed in STRING. With z/OS® XL C/C++, the string passed to the regexec() function is assumed to be in the initial shift state, unless REG_NOTBOL is specified. If REG_NOTBOL is specified, the shift state used is the shift state after the last call to the regexec() function. The information returned by the regexec() function in the regmatch_t structure has the shift-state at the start and end of the string added. This will assist an application to perform replacements or processing of the partial string. To perform replacements, the application must add the required shift-out and shift-in characters where necessary. No library functions are available to assist the application. If MB_CUR_MAX is specified as 4, but the charmap file does not specify the DBCS characters, and a collating-element (for example, [:a:]) is specified in the pattern, the DBCS characters will not match against the collating-element even if they have an equivalent weight to the collating-element.
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/* This example compiles an extended regular expression, and match against a string. */ #include <regex.h> #include <locale.h> #include <stdio.h> #include <stdlib.h> main() { regex_t preg; char *string = "a simple string"; char *pattern = ".*(simple).*"; int rc; size_t nmatch = 2; regmatch_t pmatch[2]; if ((rc = regcomp(&preg, pattern, REG_EXTENDED)) != 0) { printf("regcomp() failed, returning nonzero (%d)\n", rc); exit(1); } if ((rc = regexec(&preg, string, nmatch, pmatch, 0)) != 0) { printf("failed to ERE match '%s' with '%s',returning %d.\n", string, pattern, rc); } regfree(&preg); }
printf() Function in C
Writes the C string pointed by format to the standard output (stdout). If format includes format specifiers (subsequences beginning with %), the additional arguments following format are formatted and inserted in the resulting string replacing their respective specifiers. printf format string refers to a control parameter used by a class of functions in the input/output libraries of C programming language. The string is written in a simple template language: characters are usually copied literally into the function's output, but format specifiers, which start with a % character, indicate the location and method to translate a piece of data (such as a number) to characters. "printf" is the name of one of the main C output functions, and stands for "print formatted". printf format strings are complementary to scanf format strings, which provide formatted input (parsing). In both cases these provide simple functionality and fixed format compared to more sophisticated and flexible template engines or parsers, but are sufficient for many purposes.
Syntax for printf() function in C
#include <stdio.h> int printf ( const char * format, ... );
format
C string that contains the text to be written to stdout. It can optionally contain embedded format specifiers that are replaced by the values specified in subsequent additional arguments and formatted as requested. A format specifier follows this prototype: [see compatibility note below] %[flags][width][.precision][length]specifier Where the specifier character at the end is the most significant component, since it defines the type and the interpretation of its corresponding argument:
specifier
a conversion format specifier.
d or i
Signed decimal integer
u
Unsigned decimal integer
o
Unsigned octal
x
Unsigned hexadecimal integer
X
Unsigned hexadecimal integer (uppercase)
f
Decimal floating point, lowercase
F
Decimal floating point, uppercase
e
Scientific notation (mantissa/exponent), lowercase
E
Scientific notation (mantissa/exponent), uppercase
g
Use the shortest representation: %e or %f
G
Use the shortest representation: %E or %F
a
Hexadecimal floating point, lowercase
A
Hexadecimal floating point, uppercase
c
Character
s
String of characters
p
Pointer address
n
Nothing printed. The corresponding argument must be a pointer to a signed int. The number of characters written so far is stored in the pointed location.
%
A % followed by another % character will write a single % to the stream. The format specifier can also contain sub-specifiers: flags, width, .precision and modifiers (in that order), which are optional and follow these specifications:
flags
one or more flags that modifies the conversion behavior (optional)
-
Left-justify within the given field width; Right justification is the default (see width sub-specifier).
+
Forces to preceed the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign.
(space)
If no sign is going to be written, a blank space is inserted before the value.
#
Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values different than zero. Used with a, A, e, E, f, F, g or G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written.
0
Left-pads the number with zeroes (0) instead of spaces when padding is specified (see width sub-specifier).
width
an optional * or integer value used to specify minimum width field.
(number)
Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.
*
The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
.precision
an optional field consisting of a . followed by * or integer or nothing to specify the precision.
.number
For integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0. For a, A, e, E, f and F specifiers: this is the number of digits to be printed after the decimal point (by default, this is 6). For g and G specifiers: This is the maximum number of significant digits to be printed. For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered. If the period is specified without an explicit value for precision, 0 is assumed.
.*
The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
length
an optional length modifier that specifies the size of the argument.
... (additional arguments)
Depending on the format string, the function may expect a sequence of additional arguments, each containing a value to be used to replace a format specifier in the format string (or a pointer to a storage location, for n). There should be at least as many of these arguments as the number of values specified in the format specifiers. Additional arguments are ignored by the function. If a writing error occurs, the error indicator (ferror) is set and a negative number is returned. If a multibyte character encoding error occurs while writing wide characters, errno is set to EILSEQ and a negative number is returned.
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/* print formatted data to stdout by printf() function example */ #include <stdio.h> int main() { char ch; char str[100]; int a; float b; printf("Enter any character \n"); scanf("%c", &ch); printf("Entered character is %c \n", ch); printf("Enter any string ( upto 100 character ) \n"); scanf("%s", &str); printf("Entered string is %s \n", str); printf("Enter integer and then a float: "); // Taking multiple inputs scanf("%d%f", &a, &b); printf("You entered %d and %f", a, b); return 0; }
Switch Case Statement in C
Switch statement in C tests the value of a variable and compares it with multiple cases. Once the case match is found, a block of statements associated with that particular case is executed. Each case in a block of a switch has a different name/number which is referred to as an identifier. The value provided by the user is compared with all the cases inside the switch block until the match is found. If a case match is NOT found, then the default statement is executed, and the control goes out of the switch block.
Syntax for Switch Case Statement in C
switch(expression) { case constant-expression : statement(s); break; /* optional */ case constant-expression : statement(s); break; /* optional */ /* you can have any number of case statements */ default : /* Optional */ statement(s); }
• The expression used in a switch statement must have an integral or enumerated type, or be of a class type in which the class has a single conversion function to an integral or enumerated type. • You can have any number of case statements within a switch. Each case is followed by the value to be compared to and a colon. • The constant-expression for a case must be the same data type as the variable in the switch, and it must be a constant or a literal. • When the variable being switched on is equal to a case, the statements following that case will execute until a break statement is reached. • When a break statement is reached, the switch terminates, and the flow of control jumps to the next line following the switch statement. • Not every case needs to contain a break. If no break appears, the flow of control will fall through to subsequent cases until a break is reached. • A switch statement can have an optional default case, which must appear at the end of the switch. The default case can be used for performing a task when none of the cases is true. No break is needed in the default case.
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/* switch case statement in C language*/ // Program to create a simple calculator #include <stdio.h> int main() { char operation; double n1, n2; printf("Enter an operator (+, -, *, /): "); scanf("%c", &operation); printf("Enter two operands: "); scanf("%lf %lf",&n1, &n2); switch(operation) { case '+': printf("%.1lf + %.1lf = %.1lf",n1, n2, n1+n2); break; case '-': printf("%.1lf - %.1lf = %.1lf",n1, n2, n1-n2); break; case '*': printf("%.1lf * %.1lf = %.1lf",n1, n2, n1*n2); break; case '/': printf("%.1lf / %.1lf = %.1lf",n1, n2, n1/n2); break; // operator doesn't match any case constant +, -, *, / default: printf("Error! operator is not correct"); } return 0; }
fprintf() Function in C
Write formatted data to stream. Writes the C string pointed by format to the stream. If format includes format specifiers (subsequences beginning with %), the additional arguments following format are formatted and inserted in the resulting string replacing their respective specifiers. After the format parameter, the function expects at least as many additional arguments as specified by format.
Syntax for fprintf() Function in C
#include <stdio.h> int fprintf ( FILE * stream, const char * format, ... );
stream
Pointer to a FILE object that identifies an output stream.
format
C string that contains the text to be written to the stream. It can optionally contain embedded format specifiers that are replaced by the values specified in subsequent additional arguments and formatted as requested. A format specifier follows this prototype: %[flags][width][.precision][length]specifier Where the specifier character at the end is the most significant component, since it defines the type and the interpretation of its corresponding argument:
specifier
a conversion format specifier.
d or i
Signed decimal integer
u
Unsigned decimal integer
o
Unsigned octal
x
Unsigned hexadecimal integer
X
Unsigned hexadecimal integer (uppercase)
f
Decimal floating point, lowercase
F
Decimal floating point, uppercase
e
Scientific notation (mantissa/exponent), lowercase
E
Scientific notation (mantissa/exponent), uppercase
g
Use the shortest representation: %e or %f
G
Use the shortest representation: %E or %F
a
Hexadecimal floating point, lowercase
A
Hexadecimal floating point, uppercase
c
Character
s
String of characters
p
Pointer address
n
Nothing printed. The corresponding argument must be a pointer to a signed int. The number of characters written so far is stored in the pointed location.
%
A % followed by another % character will write a single % to the stream. The format specifier can also contain sub-specifiers: flags, width, .precision and modifiers (in that order), which are optional and follow these specifications:
flags
one or more flags that modifies the conversion behavior (optional)
-
Left-justify within the given field width; Right justification is the default (see width sub-specifier).
+
Forces to preceed the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign.
(space)
If no sign is going to be written, a blank space is inserted before the value.
#
Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values different than zero. Used with a, A, e, E, f, F, g or G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written.
0
Left-pads the number with zeroes (0) instead of spaces when padding is specified (see width sub-specifier).
width
an optional * or integer value used to specify minimum width field.
(number)
Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.
*
The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
.precision
an optional field consisting of a . followed by * or integer or nothing to specify the precision.
.number
For integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0. For a, A, e, E, f and F specifiers: this is the number of digits to be printed after the decimal point (by default, this is 6). For g and G specifiers: This is the maximum number of significant digits to be printed. For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered. If the period is specified without an explicit value for precision, 0 is assumed.
.*
The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
length
an optional length modifier that specifies the size of the argument.
h
The argument is interpreted as a short int or unsigned short int (only applies to integer specifiers: i, d, o, u, x and X).
l
The argument is interpreted as a long int or unsigned long int for integer specifiers (i, d, o, u, x and X), and as a wide character or wide character string for specifiers c and s.
L
The argument is interpreted as a long double (only applies to floating point specifiers - e, E, f, g and G).
... (additional arguments)
Depending on the format string, the function may expect a sequence of additional arguments, each containing a value to be used to replace a format specifier in the format string (or a pointer to a storage location, for n). There should be at least as many of these arguments as the number of values specified in the format specifiers. Additional arguments are ignored by the function. On success, the total number of characters written is returned. If a writing error occurs, the error indicator (ferror) is set and a negative number is returned. If a multibyte character encoding error occurs while writing wide characters, errno is set to EILSEQ and a negative number is returned.
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/* write the C string pointed by format to the stream by fprintf() function example */ #include <stdio.h> void main() { FILE *fptr; int id; char name[30]; float salary; fptr = fopen("emp.txt", "w+");/* open for writing */ if (fptr == NULL) { printf("File does not exists \n"); return; } printf("Enter the id\n"); scanf("%d", &id); fprintf(fptr, "Id= %d\n", id); printf("Enter the name \n"); scanf("%s", name); fprintf(fptr, "Name= %s\n", name); printf("Enter the salary\n"); scanf("%f", &salary); fprintf(fptr, "Salary= %.2f\n", salary); fclose(fptr); }
gets() Function in C
Get string from stdin. Reads characters from the standard input (stdin) and stores them as a C string into str until a newline character or the end-of-file is reached. The newline character, if found, is not copied into str. A terminating null character is automatically appended after the characters copied to str. Notice that gets is quite different from fgets: not only gets uses stdin as source, but it does not include the ending newline character in the resulting string and does not allow to specify a maximum size for str (which can lead to buffer overflows). The gets() function enables the user to enter some characters followed by the enter key. All the characters entered by the user get stored in a character array. The null character is added to the array to make it a string. The gets() allows the user to enter the space-separated strings. It returns the string entered by the user.
Syntax for gets() Function in C
#include<stdio.h> char * gets ( char * str );
str
Pointer to a block of memory (array of char) where the string read is copied as a C string. On success, the function returns str. If the end-of-file is encountered while attempting to read a character, the eof indicator is set (feof). If this happens before any characters could be read, the pointer returned is a null pointer (and the contents of str remain unchanged). If a read error occurs, the error indicator (ferror) is set and a null pointer is also returned (but the contents pointed by str may have changed).
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/* read characters from the standard input (stdin) and stores them as a C string */ #include<stdio.h> #include<conio.h> #include<stdlib.h> void main() { clrscr(); FILE *fp; char fname[20]; printf("Enter filename : "); gets(fname); fp=fopen(fname, "r"); if(fp==NULL) { printf("Error in opening the file..!!\n"); printf("Press any key to exit..\n"); getch(); exit(1); } fclose(fp); getch(); }
If Else If Ladder in C/C++
The if...else statement executes two different codes depending upon whether the test expression is true or false. Sometimes, a choice has to be made from more than 2 possibilities. The if...else ladder allows you to check between multiple test expressions and execute different statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
Syntax of if...else Ladder in C
if (Condition1) { Statement1; } else if(Condition2) { Statement2; } . . . else if(ConditionN) { StatementN; } else { Default_Statement; }
In the above syntax of if-else-if, if the Condition1 is TRUE then the Statement1 will be executed and control goes to next statement in the program following if-else-if ladder. If Condition1 is FALSE then Condition2 will be checked, if Condition2 is TRUE then Statement2 will be executed and control goes to next statement in the program following if-else-if ladder. Similarly, if Condition2 is FALSE then next condition will be checked and the process continues. If all the conditions in the if-else-if ladder are evaluated to FALSE, then Default_Statement will be executed.
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/* write a C program which demonstrate use of if-else-if ladder statement */ #include<stdio.h> #include<conio.h> void main() { int a; printf("Enter a Number: "); scanf("%d",&a); if(a > 0) { printf("Given Number is Positive"); } else if(a == 0) { printf("Given Number is Zero"); } else if(a < 0) { printf("Given Number is Negative"); } getch(); }


C Programming code finding the transpose of a martix in sparse form. Printing for testing sparse input. Calling function for evaluation of transpose. Printing the transposed matrix.