exit() Function in C with Example

This tutorial explains the exit() function in C and how it is used.

The exit() function is useful to terminate a program after detecting an error that prevents the program from continuing to run normally. The prototype is as follows:

    void exit(int status);

• Status argument passed to exit() is returned to O.S. to inform that whether or not program succeeded normally.
• Notice that this status argument is as same as status main() passes to O.S. Pre defined symbols EXIT_SUCCESS and EXIT_FAILURE are used to pass successful and failure status to O.S respectively.
• exit() function is prototyped in stdlib.h header file.

A fragment of code from stdlib.h defining EXIT_SUCCESS and EXIT_FAILURE is copied below for ref.

/* We define these the same for all machines.
   Changes from this to the outside world should be done in `_exit'.  */
#define EXIT_FAILURE    1       /* Failing exit status.  */
#define EXIT_SUCCESS    0       /* Successful exit status.  */

Notice that other values could also be used to pass to exit() but their meaning is implementation dependent. It’s a good programming practice to follow calls to perror() with a call to exit().

Let’s take a simple C program to understand the behaviour of exit() function in C,

/* exit.c -- program unravels exit() behaviour */
#include <stdio.h>
#include <stdlib.h>
 
int main(int argc, char *argv[])
{
    FILE *fp;
 
    /* test if file to be opened is given on command line */
    if (argc == 2) {
        fp = fopen(argv[1], "r");
 
        if (fp == NULL) {
            perror("File Open");
            exit(EXIT_FAILURE);
        }
        else {
            printf("File: \"%s\" opened successfully!\n", argv[1]);
        }
    }
    else {
        /* if the file argument is not given or more than */
        /* 2 arguments are given */
        puts("Error File Argument");
        exit(EXIT_FAILURE);
    }
 
    return 0;
}

Let’s turn ours’ attention to the output below

[root@localhost ch15_Input_Output_Functions]# ./a.out preeti.txt
File: "preeti.txt" opened successfully!
[root@localhost ch15_Input_Output_Functions]# ./a.out
Error File Argument
[root@localhost ch15_Input_Output_Functions]# ./a.out preeti
File Open: No such file or directory

Notice that this function never returns. When exit() function is completed, the program has disappeared and there’s nothing to return to.

Sanfoundry Global Education & Learning Series – 1000 C Tutorials.