C Error Handling - Introduction to errno


Introduction

Error handling is a critical aspect of programming, and in C, the global variable 

errno
plays a significant role in reporting and identifying errors. It helps you understand the nature of errors that occur during function calls and file operations. In this guide, we'll introduce the concept of C error handling using 
errno
, explain its purpose, and provide sample code to illustrate its usage.


The Role of errno

errno
is a global integer variable that is part of the C Standard Library. It is used to store error codes that indicate the cause of errors in C programs. When functions or system calls encounter an error, they typically set the value of 
errno
to a specific error code that corresponds to the type of error encountered. By checking the value of 
errno
, you can determine the nature of the error and take appropriate action.


Sample Code

Let's explore some examples of using 

errno
in C:


Reading from a Non-Existent File

#include <stdio.h>
#include <errno.h>
int main() {
    FILE *file = fopen("nonexistent_file.txt", "r");
    if (file == NULL) {
printf("Error opening the file. Error code: %d\\n", errno);
    }
    return 0;
}

Handling Division by Zero

#include <stdio.h>
#include <errno.h>
#include <math.h>
int main() {
    double result;
    result = 1.0 / 0.0; // Attempting division by zero
    if (errno == EDOM) {
printf("Error: Division by zero. Error code: %d\\n", errno);
errno = 0; // Reset errno
    } else {
printf("Result: %f\\n", result);
    }
    return 0;
}

Conclusion

Error handling using 

errno
is a crucial part of C programming, allowing you to identify and respond to errors effectively. This guide introduced the concept of C error handling with 
errno
, explained its purpose, and provided sample code to demonstrate its usage. As you continue your C programming journey, you'll find 
errno
to be a valuable tool for handling errors gracefully.