Error Handling in C Language

Introduction

Error handling is a critical aspect of software development, ensuring that the program can handle unexpected situations gracefully. In C programming, error handling can be achieved using various strategies, including return codes, errno, and setjmp/longjmp. This tutorial will cover these methods in detail with examples.

Return Codes

One of the simplest ways to handle errors in C is by using return codes. Functions return specific values to indicate success or failure.

#include <stdio.h>

int divide(int a, int b, int *result) {
    if (b == 0) {
        return -1; // Error code for division by zero
    } else {
        *result = a / b;
        return 0; // Success
    }
}

int main() {
    int result;
    int status = divide(10, 2, &result);

    if (status == 0) {
        printf("Result: %d\n", result);
    } else {
        printf("Error: Division by zero\n");
    }

    return 0;
}
                

Using errno

The errno variable is a global variable set by system calls and some library functions in the event of an error to indicate what went wrong.

#include <stdio.h>
#include <errno.h>
#include <string.h>

int main() {
    FILE *fp = fopen("nonexistentfile.txt", "r");

    if (fp == NULL) {
        printf("Error opening file: %s\n", strerror(errno));
    } else {
        // File operations
        fclose(fp);
    }

    return 0;
}
                

setjmp and longjmp

The setjmp and longjmp functions provide a way to handle errors by jumping back to a specific point in the program. This can be useful for error recovery.

#include <stdio.h>
#include <setjmp.h>

jmp_buf buf;

void error_function() {
    printf("Error: Something went wrong!\n");
    longjmp(buf, 1);
}

int main() {
    if (setjmp(buf)) {
        printf("Recovered from error\n");
    } else {
        error_function();
    }

    return 0;
}
                

Best Practices

Here are some best practices for error handling in C:

• Always check the return values of functions that can fail.
• Use errno to get more information about errors when using system calls or library functions.
• Avoid using setjmp and longjmp unless absolutely necessary, as they can make code harder to understand and maintain.
• Provide meaningful error messages to help diagnose issues.