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C Programming Code Examples

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Program to get the GroupID ( GID ) information

/* Program to get the GroupID ( GID ) information */ #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/types.h> int main() { gid_t gid; if ((gid = getgid()) < 0) { perror(" getgid error"); } else { printf(" The group id is : %d", gid); } if ((gid = getegid()) < 0) { perror(" getegid error"); } else { printf(" The effective group id is : %d", gid); } printf(" "); return(0); }

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.

getgid() returns the real group ID of the calling process. getegid() returns the effective group ID of the calling process. The getegid() function shall always be successful and no return value is reserved to indicate an error. The original Linux getgid() and getegid() system calls supported only 16-bit group IDs. Subsequently, Linux 2.4 added getgid32() and getegid32(), supporting 32-bit IDs. The glibc getgid() and getegid() wrapper functions transparently deal with the variations across kernel versions. On Alpha, instead of a pair of getgid() and getegid() system calls, a single getxgid() system call is provided, which returns a pair of real and effective GIDs. The glibc getgid() and getegid() wrapper functions transparently deal with this.

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,

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.

#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:

The if-else statement is used to perform two operations for a single condition. The if-else statement is an extension to the if statement using which, we can perform two different operations, i.e., one is for the correctness of that condition, and the other is for the incorrectness of the condition. Here, we must notice that if and else block cannot be executed simiulteneously. Using if-else statement is always preferable since it always invokes an otherwise case with every if condition.

C Program Code Bitwise operators During computation, mathematical operations like: addition, subtraction, addition and division are converted to bit-level which makes and

Program to check Vowel or Consonant using switch-case statement. I already explained in sample to print number of days in months, if switch case contains same action for multiple