File I/O Errors

• The "<errno.h>" is a header file in the C programming language that is used to define several error codes and functions related to error handling. It is part of the C standard library and provides a standardized way to report and handle errors that occur during program execution.

Handling Errors

Handling errors during file processing in C is essential to ensure the robustness and reliability of your program. Errors can occur for various reasons, such as the file not existing, permission issues, or other I/O problems. To handle these errors, you can use techniques like error checking, error codes, and proper error messages. Here's a general approach to handle errors during file processing in C:

• Include necessary header files:

Make sure to include the required header files, such as "<stdio.h>", which provides functions for file I/O, and "<errno.h>", which contains error codes and messages.

• Open the file using 'fopen':

Use the 'fopen' function to open the file. Check if it returns a valid file pointer (not 'NULL') to ensure that the file was opened successfully.

FILE* file = fopen("myfile.txt", "r");
if (file == NULL) {
    perror("Error opening the file");
    // Handle the error or exit the program
    exit(EXIT_FAILURE);
}

• Perform file operations:

Perform read or write operations on the file using functions like 'fread', 'fwrite', 'fprintf', etc.

• Check for errors:

After performing file operations, you should check for errors by examining the value of 'errno'. If an error occurred, you can handle it accordingly.

if (ferror(file)) {
    perror("Error during file operation");
    // Handle the error or exit the program
    exit(EXIT_FAILURE);
}

• Close the file::

Always close the file when you're done with it. Use the 'fclose' function.

if (fclose(file) != 0) {
    perror("Error closing the file");
    // Handle the error or exit the program
    exit(EXIT_FAILURE);
}

• Handle specific error cases:

Depending on your application, you may want to handle specific error cases more gracefully. For example, you can check for errors related to specific file operations or handle cases where the file doesn't exist.

Here's an example of how to handle a specific error, such as a file not existing:

if (errno == ENOENT) {
    fprintf(stderr, "The file does not exist\n");
    // Handle the error or exit the program
    exit(EXIT_FAILURE);
}

Now, let's create a C program where we handle errors during file processing:

example.txt

The file opened & read successfully.

main.c

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

int main() {
    FILE* file = fopen("example.txt", "r");
    
    if (file == NULL) {
        perror("Error opening the file");
        exit(EXIT_FAILURE);
    }

    char buffer[100];
    while (fgets(buffer, sizeof(buffer), file) != NULL) {
        if (ferror(file)) {
            perror("Error reading from the file");
            fclose(file);
            exit(EXIT_FAILURE);
        }

        // Process the data from the file (e.g., print it)
        printf("Read: %s", buffer);
    }

    if (fclose(file) != 0) {
        perror("Error closing the file");
        exit(EXIT_FAILURE);
    }

    return 0;
}

Note: The 'fgets()' and 'fputs()' are also standard I/O functions in the C programming language for reading and writing text in files or from/to streams. They are often used together to read and write text data in C programs.

This program provides error handling at each step, ensuring that any errors during file processing are properly reported and handled. Make sure you have a file named "example.txt" in the same directory as the program for this example to work.

Read: The file opened & read successfully.

* In this program 'buffer' is an array of characters used to temporarily store the data read from the file "example.txt" using the 'fgets' function.