Understanding exit(), abort(), and assert() in C

In C programming, process termination functions play a crucial role in handling program execution flow. This article explores three important functions: exit(), abort(), and assert(), explaining their differences and use cases.

1. exit() in C

The exit() function terminates a program normally and returns a status code to the operating system. It ensures that system resources are properly released.

Key Operations of exit():

• Closes all open files.
• Flushes unwritten buffered data.
• Removes temporary files.
• Returns an integer exit status to the operating system.

Using atexit(), you can customize exit() to execute specific actions at program termination.

Example:

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

int main () {
    FILE *pFile;
    pFile = fopen("file1.txt", "r");
    if (pFile == NULL) {
        printf("Error opening file");
        exit(1);
    }
    else {
        /* Perform file operations */
    }
    return 0;
}

2. abort() in C

The abort() function is used to terminate a program abruptly by raising a SIGABRT signal. Unlike exit(), it does not clean up system resources such as file buffers before terminating the program.

Example:

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

int main() {
    FILE *fp = fopen("file1.txt", "w");
    if(fp == NULL) {
        printf("Could not open file\n");
        exit(1);
    }
    fprintf(fp, "%s", "Face Prep");
    /* Simulating an error */
    abort();
    return 0;
}

3. assert() in C

assert() is primarily used for debugging. It checks an expression and, if the expression evaluates to false (zero), it prints an error message and calls abort().

Key Points:

• If the assertion fails, it outputs the file name, line number, and expression.
• If NDEBUG is defined (#define NDEBUG), assertions are disabled.

Example:

#include <assert.h>

void open_record(char *record_name) {
    assert(record_name != NULL);
    /* Rest of the code */
}

int main(void) {
    open_record(NULL); // This will trigger an assertion failure
    return 0;
}

Conclusion

• Use exit() when you want to terminate a program gracefully, ensuring proper resource cleanup.
• Use abort() when an unexpected error occurs, and you need immediate termination.
• Use assert() for debugging to catch logical errors during development.