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C Programming Code Examples

C > Small Programs Code Examples

Filter text with a stop word list

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/* Filter text with a stop word list */ #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAXTOKENS 256 #define MAXLINE 1024 #define MINLEN 3 #define STMINLEN 2 struct tnode { char *word; int count; struct tnode *left, *right; }; struct tnode *buildstoptree(char *, struct tnode *); struct tnode *addtree(struct tnode *, char *); struct tnode *findstopword(struct tnode *, char *); struct tnode *talloc(void); void freetree(struct tnode *); char **split(char *, char *); int main(int argc, char *argv[]) { /* delim does not include \' [\047] quote */ char *delim = ".,:;`\"+-_(){}[]<>*&^%$#@!?~/|\\= \t\r\n1234567890"; char **tokens = NULL; struct tnode *root = {0}; struct tnode *querry = {0}; char line[MAXLINE]; int i = 0; if(argc != 2) { fprintf(stderr, "Usage: tokstop STOPLIST.txt\n"); return 1; } root = buildstoptree(argv[1], root); if(root == NULL) return 1; while(fgets(line, MAXLINE, stdin) != NULL) { if(strlen(line) < MINLEN) continue; tokens = split(line, delim); for(i = 0; tokens[i] != NULL; i++) { querry = findstopword(root, tokens[i]); if(querry == NULL) printf("%s ", tokens[i]); } for(i = 0; tokens[i] != NULL; i++) free(tokens[i]); free(tokens[i]); printf("\n"); } freetree(root); return 0; } /* read stoplist into binary tree, expects one entry per line */ struct tnode *buildstoptree(char *fname, struct tnode *p) { FILE *fp = {0}; char line[MAXLINE]; int len = 0, lcount = 0; fp = fopen(fname, "r"); if(fp == NULL) { fprintf(stderr, "Error - fopen(%s)\n", fname); return NULL; } while(fgets(line, MAXLINE, fp) != NULL) { len = strlen(line); if(len < STMINLEN) continue; else lcount++; if(line[len - 1] == '\n') line[--len] = '\0'; p = addtree(p, line); } if(lcount == 0) { fprintf(stderr, "Error - Zero stopwords..\n"); return NULL; } fclose(fp); return p; } /* split string into tokens, return token array */ char **split(char *string, char *delim) { char **tokens = NULL; char *working = NULL; char *token = NULL; int idx = 0; tokens = malloc(sizeof(char *) * MAXTOKENS); if(tokens == NULL) return NULL; working = malloc(sizeof(char) * strlen(string) + 1); if(working == NULL) return NULL; /* to make sure, copy string to a safe place */ strcpy(working, string); for(idx = 0; idx < MAXTOKENS; idx++) tokens[idx] = NULL; token = strtok(working, delim); idx = 0; /* always keep the last entry NULL terminated */ while((idx < (MAXTOKENS - 1)) && (token != NULL)) { tokens[idx] = malloc(sizeof(char) * strlen(token) + 1); if(tokens[idx] != NULL) { strcpy(tokens[idx], token); idx++; token = strtok(NULL, delim); } } free(working); return tokens; } /* install word in binary tree */ struct tnode *addtree(struct tnode *p, char *w) { int cond; if(p == NULL) { p = talloc(); p->word = strdup(w); p->count = 1; p->left = p->right = NULL; } else if((cond = strcmp(w, p->word)) == 0) p->count++; else if(cond < 0) p->left = addtree(p->left, w); else p->right = addtree(p->right, w); return p; } /* make new tnode */ struct tnode *talloc(void) { return(struct tnode *)malloc(sizeof(struct tnode)); } /* find value w in binary tree */ struct tnode *findstopword(struct tnode *p, char *w) { struct tnode *temp; int cond = 0; temp = p; while(temp != NULL) { if((cond = strcmp(temp->word, w)) == 0) return temp; else if(cond > 0) temp = temp->left; else temp = temp->right; } return NULL; } /* free binary tree */ void freetree(struct tnode *p) { if(p != NULL) { free(p->left); free(p->right); free(p->word); free(p); } }
fopen() Function in C
Open file. Opens the file whose name is specified in the parameter filename and associates it with a stream that can be identified in future operations by the FILE pointer returned. The operations that are allowed on the stream and how these are performed are defined by the mode parameter. The returned stream is fully buffered by default if it is known to not refer to an interactive device (see setbuf). The returned pointer can be disassociated from the file by calling fclose or freopen. All opened files are automatically closed on normal program termination. The running environment supports at least FOPEN_MAX files open simultaneously.
Syntax for fopen() Function in C
#include <stdio.h> FILE * fopen ( const char * filename, const char * mode );
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).
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. Text files are files containing sequences of lines of text. Depending on the environment where the application runs, some special character conversion may occur in input/output operations in text mode to adapt them to a system-specific text file format. Although on some environments no conversions occur and both text files and binary files are treated the same way, using the appropriate mode improves portability. For files open for update (those which include a "+" sign), on which both input and output operations are allowed, the stream shall be flushed (fflush) or repositioned (fseek, fsetpos, rewind) before a reading operation that follows a writing operation. The stream shall be repositioned (fseek, fsetpos, rewind) before a writing operation that follows a reading operation (whenever that operation did not reach the end-of-file). If the file is successfully opened, the function returns a pointer to a FILE object that can be used to identify the stream on future operations. 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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/* open the file specified by filename and associates a stream with it by fopen() 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; }
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; }
#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; }
malloc() Function in C
Allocate memory block. Allocates a block of size bytes of memory, returning a pointer to the beginning of the block. The content of the newly allocated block of memory is not initialized, remaining with indeterminate values. If size is zero, the return value depends on the particular library implementation (it may or may not be a null pointer), but the returned pointer shall not be dereferenced. The "malloc" or "memory allocation" method in C is used to dynamically allocate a single large block of memory with the specified size. It returns a pointer of type void which can be cast into a pointer of any form. It doesn't Iniatialize memory at execution time so that it has initializes each block with the default garbage value initially.
Syntax for malloc() Function in C
#include <stdlib.h> void* malloc (size_t size);
size
Size of the memory block, in bytes. size_t is an unsigned integral type. On success, function returns a pointer to the memory block allocated by the function. The type of this pointer is always void*, which can be cast to the desired type of data pointer in order to be dereferenceable. If the function failed to allocate the requested block of memory, a null pointer is returned.
Data races
Only the storage referenced by the returned pointer is modified. No other storage locations are accessed by the call. If the function reuses the same unit of storage released by a deallocation function (such as free or realloc), the functions are synchronized in such a way that the deallocation happens entirely before the next allocation.
Exceptions
No-throw guarantee: this function never throws exceptions.
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/* allocate memory block by malloc() function example */ // Program to calculate the sum of n numbers entered by the user #include <stdio.h> #include <stdlib.h> int main() { int n, i, *ptr, sum = 0; printf("Enter number of elements: "); scanf("%d", &n); ptr = (int*) malloc(n * sizeof(int)); // if memory cannot be allocated if(ptr == NULL) { printf("Error! memory not allocated."); exit(0); } printf("Enter elements: "); for(i = 0; i < n; ++i) { scanf("%d", ptr + i); sum += *(ptr + i); } printf("Sum = %d", sum); // deallocating the memory free(ptr); 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" ); } }
What is an Array in C Language
An array is defined as the collection of similar type of data items stored at contiguous memory locations. Arrays are the derived data type in C programming language which can store the primitive type of data such as int, char, double, float, etc. It also has the capability to store the collection of derived data types, such as pointers, structure, etc. The array is the simplest data structure where each data element can be randomly accessed by using its index number. C array is beneficial if you have to store similar elements. For example, if we want to store the marks of a student in 6 subjects, then we don't need to define different variables for the marks in the different subject. Instead of that, we can define an array which can store the marks in each subject at the contiguous memory locations. By using the array, we can access the elements easily. Only a few lines of code are required to access the elements of the array.
Properties of Array
The array contains the following properties. • Each element of an array is of same data type and carries the same size, i.e., int = 4 bytes. • Elements of the array are stored at contiguous memory locations where the first element is stored at the smallest memory location. • Elements of the array can be randomly accessed since we can calculate the address of each element of the array with the given base address and the size of the data element.
Advantage of C Array
• 1) Code Optimization: Less code to the access the data. • 2) Ease of traversing: By using the for loop, we can retrieve the elements of an array easily. • 3) Ease of sorting: To sort the elements of the array, we need a few lines of code only. • 4) Random Access: We can access any element randomly using the array.
Disadvantage of C Array
• 1) Allows a fixed number of elements to be entered which is decided at the time of declaration. Unlike a linked list, an array in C is not dynamic. • 2) Insertion and deletion of elements can be costly since the elements are needed to be managed in accordance with the new memory allocation.
Declaration of C Array
To declare an array in C, a programmer specifies the type of the elements and the number of elements required by an array as follows
type arrayName [ arraySize ];
This is called a single-dimensional array. The arraySize must be an integer constant greater than zero and type can be any valid C data type. For example, to declare a 10-element array called balance of type double, use this statement
double balance[10];
Here balance is a variable array which is sufficient to hold up to 10 double numbers.
Initializing Arrays
You can initialize an array in C either one by one or using a single statement as follows
double balance[5] = {850, 3.0, 7.4, 7.0, 88};
The number of values between braces { } cannot be larger than the number of elements that we declare for the array between square brackets [ ]. If you omit the size of the array, an array just big enough to hold the initialization is created. Therefore, if you write
double balance[] = {850, 3.0, 7.4, 7.0, 88};
Accessing Array Elements
An element is accessed by indexing the array name. This is done by placing the index of the element within square brackets after the name of the array.
double salary = balance[9];
The above statement will take the 10th element from the array and assign the value to salary variable.
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/* arrays in C Language */ #include<stdio.h> void main () { int i, j,temp; int a[10] = { 4, 8, 16, 120, 36, 44, 13, 88, 90, 23}; for(i = 0; i<10; i++) { for(j = i+1; j<10; j++) { if(a[j] > a[i]) { temp = a[i]; a[i] = a[j]; a[j] = temp; } } } printf("Printing Sorted Element List ...\n"); for(i = 0; i<10; i++) { printf("%d\n",a[i]); } }
free() Function in C
The free() function in C library allows you to release or deallocate the memory blocks which are previously allocated by calloc(), malloc() or realloc() functions. It frees up the memory blocks and returns the memory to heap. It helps freeing the memory in your program which will be available for later use. In C, the memory for variables is automatically deallocated at compile time. For dynamic memory allocation in C, you have to deallocate the memory explicitly. If not done, you may encounter out of memory error.
Syntax for free() Function in C
#include<stdlib.h> void free(void *ptr).
ptr
This is the pointer to a memory block previously allocated with malloc, calloc or realloc to be deallocated. If a null pointer is passed as argument, no action occurs. This function does not return any value.
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/* deallocate memory block by free() function example */ #include <stdio.h> #include <stdlib.h> #include <string.h> int main () { char *str; /* Initial memory allocation */ str = (char *) malloc(15); strcpy(str, "HappyCodings"); printf("String = %s, Address = %u\n", str, str); /* Reallocating memory */ str = (char *) realloc(str, 25); strcat(str, ".com"); printf("String = %s, Address = %u\n", str, str); /* Deallocate allocated memory */ free(str); 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; }
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; }
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; }
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; }
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; }
strcmp() Function in C
Compare two strings. Compares the C string str1 to the C string str2. This function starts comparing the first character of each string. If they are equal to each other, it continues with the following pairs until the characters differ or until a terminating null-character is reached. This function performs a binary comparison of the characters. For a function that takes into account locale-specific rules, see strcoll.
Syntax for strcmp() Function in C
#include <string.h> int strcmp ( const char * str1, const char * str2 );
str1
C string to be compared.
str2
C string to be compared. Function returns an integral value indicating the relationship between the strings: • <0 the first character that does not match has a lower value in ptr1 than in ptr2 • 0 the contents of both strings are equal • >0 the first character that does not match has a greater value in ptr1 than in ptr2 The strcmp() function is used to compare two strings two strings str1 and str2. If two strings are same then strcmp() returns 0, otherwise, it returns a non-zero value. This function compares strings character by character using ASCII value of the characters. The comparison stops when either end of the string is reached or corresponding characters are not same. The non-zero value returned on mismatch is the difference of the ASCII values of the non-matching characters of two strings.
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/* compare two strings and return an integer value based on the result by strcmp() function example. */ #include <stdio.h> #include <string.h> int main () { char str1[15]; char str2[15]; int ret; strcpy(str1, "abcdef"); strcpy(str2, "ABCDEF"); ret = strcmp(str1, str2); if(ret < 0) { printf("str1 is less than str2"); } else if(ret > 0) { printf("str2 is less than str1"); } else { printf("str1 is equal to str2"); } 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; }
sizeof() Operator in C
The sizeof() operator is commonly used in C. It determines the size of the expression or the data type specified in the number of char-sized storage units. The sizeof() operator contains a single operand which can be either an expression or a data typecast where the cast is data type enclosed within parenthesis. The data type cannot only be primitive data types such as integer or floating data types, but it can also be pointer data types and compound data types such as unions and structs.
Syntax for sizeof() Operator in C
#include <stdio.h> sizeof (data type)
data type
Where data type is the desired data type including classes, structures, unions and any other user defined data type. Mainly, programs know the storage size of the primitive data types. Though the storage size of the data type is constant, it varies when implemented in different platforms. For example, we dynamically allocate the array space by using sizeof() operator:
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/* return the size of a variable by sizeof() operator example */ int main( int argc, char* argv[] ) { printf("sizeof(char) = %d\n", sizeof(char) ); printf("sizeof(short) = %d\n", sizeof(short) ); printf("sizeof(int) = %d\n", sizeof(int) ); printf("sizeof(long) = %d\n", sizeof(long) ); printf("sizeof(long long) = %d\n", sizeof(long long) ); printf("\n"); printf("sizeof(unsigned char) = %d\n", sizeof(unsigned char) ); printf("sizeof(unsigned short) = %d\n", sizeof(unsigned short) ); printf("sizeof(unsigned int) = %d\n", sizeof(unsigned int) ); printf("sizeof(unsigned long) = %d\n", sizeof(unsigned long) ); printf("\n"); printf("sizeof(float) = %d\n", sizeof(float) ); printf("sizeof(double) = %d\n", sizeof(double) ); printf("sizeof(long double) = %d\n", sizeof(long double) ); printf("\n"); int x; printf("sizeof(x) = %d\n", sizeof(x) ); }
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; }
strdup() Function in C
Duplicate a specific number of bytes from a string. The strdup() function shall return a pointer to a new string, which is a duplicate of the string pointed to by str. The returned pointer can be passed to free(). A null pointer is returned if the new string cannot be created. The function strdup() is used to duplicate a string. It returns a pointer to null-terminated byte string. strdup reserves storage space for a copy of string by calling malloc. The string argument to this function is expected to contain a null character (\0) marking the end of the string.
Syntax for strdup() Function in C
#include <string.h> char* strdup( const char* str );
str
The string that you want to copy. The strdup() function shall return a pointer to a new string on success. Otherwise, it shall return a null pointer and set errno to indicate the error. Remember to free the storage reserved with the call to strdup. Strdup returns a pointer to the storage space containing the copied string. If it cannot reserve storage strdup returns NULL. strdup() function is non standard function which may not available in standard library in C.
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/* duplicate a specific number of bytes from a string by strdup() string function code example */ // C program to demonstrate strdup() #include<stdio.h> #include<string.h> int main() { char source[] = "HappyCodings"; // A copy of source is created dynamically // and pointer to copy is returned. char* target = strdup(source); printf("%s", target); return 0; }
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(); }
strcpy() Function in C
Copy string. Copies the C string pointed by source into the array pointed by destination, including the terminating null character (and stopping at that point). To avoid overflows, the size of the array pointed by destination shall be long enough to contain the same C string as source (including the terminating null character), and should not overlap in memory with source.
Syntax for strcpy() Function in C
#include <string.h> char * strcpy ( char * destination, const char * source );
destination
Pointer to the destination array where the content is to be copied.
source
C string to be copied. Destination is returned. strcpy() is a standard library function in C/C++ and is used to copy one string to another. In C it is present in string.h header file. Function copies the string pointed by source (including the null character) to the destination.
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/* copy one string to another by strcpy() function example */ #include<stdio.h> #include<string.h> int main() { char ch_arr1[20]; char ch_arr2[20]; printf("Enter first string (ch_arr_1): "); gets(ch_arr1); printf("Enter second string(ch_arr_1): "); gets(ch_arr2); printf("\nCopying first string into second... \n\n"); strcpy(ch_arr2, ch_arr1); // copy the contents of ch_arr1 to ch_arr2 printf("First string (ch_arr_1) = %s\n", ch_arr1); printf("Second string (ch_arr_2) = %s\n", ch_arr2); printf("\nCopying \"Greece\" string into ch_arr1 ... \n\n"); strcpy(ch_arr1, "Greece"); // copy Greece to ch_arr1 printf("\nCopying \"Slovenia\" string into ch_arr2 ... \n\n"); strcpy(ch_arr2, "Slovenia"); // copy Slovenia to ch_arr2 printf("First string (ch_arr_1) = %s\n", ch_arr1); printf("Second string (ch_arr_2) = %s\n", ch_arr2); // signal to operating system program ran fine return 0; }
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(); }
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; }
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; }
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; }
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); }
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; }


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