exit() vs _Exit() function in C and C++

In C, both exit() and _Exit() functions terminate a program, but they differ in how they handle cleanup operations. The exit() function performs cleanup operations before termination, while _Exit() terminates immediately without any cleanup.

Syntax

void exit(int status);
void _Exit(int status);

The exit() function calls registered cleanup functions (via atexit()), flushes buffers, and closes open streams before termination. The _Exit() function immediately terminates the program without performing any cleanup operations.

Example 1: Using exit() Function

Here's how exit() executes cleanup functions registered with atexit() −

#include <stdio.h>
#include <stdlib.h>

void my_cleanup_function(void) {
    printf("Cleanup function executed before exit\n");
}

int main() {
    atexit(my_cleanup_function);
    printf("About to call exit()\n");
    exit(0);
    printf("This line will never execute\n");
    return 0;
}

Output

About to call exit()
Cleanup function executed before exit

Example 2: Using _Exit() Function

The _Exit() function bypasses all cleanup operations −

#include <stdio.h>
#include <stdlib.h>

void my_cleanup_function(void) {
    printf("Cleanup function executed before exit\n");
}

int main() {
    atexit(my_cleanup_function);
    printf("About to call _Exit()\n");
    _Exit(0);
    printf("This line will never execute\n");
    return 0;
}

Output

About to call _Exit()

Comparison

Key Points

• Use exit() for normal program termination where cleanup is required
• Use _Exit() when immediate termination is needed without cleanup
• Both functions accept an integer status code that is returned to the operating system
• Code after either function call will never execute

Conclusion

The exit() function provides safe program termination with proper cleanup, while _Exit() offers immediate termination without cleanup. Choose exit() for normal termination and _Exit() only when cleanup operations should be avoided.