Learn Using errno for Error Reporting | Handling Runtime and System Errors

When you work with C programs that interact with the system or perform input/output operations, you may encounter situations where a function fails. The C standard library uses a global variable called errno to provide more information about such errors. The errno variable is set by library functions when an error occurs, allowing you to determine the specific cause of the failure. For instance, if you try to open a file that does not exist using fopen, the function returns NULL and sets errno to a value that indicates the reason for the error. You can then use the strerror function to convert the errno value into a human-readable error message, which is very useful for debugging and reporting errors to users.

main.c


              123456789101112
            
#include <stdio.h>
#include <errno.h>
#include <string.h>

int main() {
    FILE *file = fopen("nonexistent.txt", "r");
    if (file == NULL)
        printf("Error opening file: %s\n", strerror(errno));
    else
        fclose(file);
    return 0;
}

Everything was clear?

Thanks for your feedback!

Section 2. Chapter 3

Ask AI

Ask anything or try one of the suggested questions to begin our chat

Awesome!

Completion rate improved to 12.5

Swipe to show menu

main.c


              123456789101112
            
#include <stdio.h>
#include <errno.h>
#include <string.h>

int main() {
    FILE *file = fopen("nonexistent.txt", "r");
    if (file == NULL)
        printf("Error opening file: %s\n", strerror(errno));
    else
        fclose(file);
    return 0;
}

Everything was clear?

Thanks for your feedback!

Section 2. Chapter 3