Using goto for Exception Handling in C

Last Updated : 13 Jan, 2025

Exceptions are runtime anomalies or abnormal conditions that a program encounters during its execution. C doesn’t provide any specialized functionality for this purpose like other programming languages such as C++ or Java. However, In C, goto keyword is often used for the same purpose. The goto statement can be used to jump from anywhere to anywhere within a function.

Let’s take a look at an example:

#include <stdio.h>

int main() {
    FILE *file = NULL;

    // Attempt to open the file
    file = fopen("example.txt", "r");
    if (file == NULL) {
        printf("Error opening file\n");
            
        // Jump to the error section if the file couldn't be opened
        goto error;  
    }
    printf("File opened successfully!\n");
    fclose(file);
    return 0;

error:
  
    // Error handling section
    printf("Exiting\n");
    return 1;
}

Output

Error opening file
Exiting

Explanation: The program attempts to open a file called example.txt, and if it fails (i.e., fopen() returns NULL), it jumps to the error label using goto, prints an error message, and returns 1 to indicate failure. If successful, it prints a success message, closes the file, and returns 0.

Why Use goto for Exception Handling?

The goto statement in C provides a way to jump to a labeled part of the code. While generally discouraged in modern programming due to readability and maintainability concerns, goto can be a clean solution for error handling in specific scenarios like:

Cleaning up allocated resources.
Breaking out of nested loops or blocks.
Handling errors in a single exit path.

Examples of goto for Exception Handling

The following examples demonstrate the use of goto for exception handling in C:

Simulate try-catch Statements

The try catch statements are used for exception handling in C++ and Java.

#include <stdio.h>
int main() {
    FILE *file = NULL;
    int result = 0;

    file = fopen("example.txt", "r");
    if (file == NULL) {
        printf("Error opening file\n");
      
        // Jump to the error label if file cannot be opened
        goto error;  
    }

    // Read data (simulating an error)
    result = fread(NULL, 1, 100, file);
    if (result == 0) {
        printf("Error reading file\n");
      
        // Jump to error if reading fails
        goto error;  
    }

    // Process data (simulating a successful operation)
    printf("Successfull\n");

    // Close the file and exit
    fclose(file);
    return 0;

error:
  
    // Error handling section
    if (file != NULL) {
        fclose(file);
    }
    return 1; 
}

Output

Error opening file

Handling Exception in File Processing

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

int processFile(const char *filename) {
    FILE *file = NULL;
    char *buffer = NULL;

    // Open the file
    file = fopen(filename, "r");
    if (!file) {
        fprintf(stderr, "Error: Failed to open file '%s'\n", filename);
        goto cleanup;
    }

    // Allocate memory for the buffer
    buffer = (char *)malloc(1024);
    if (!buffer) {
        fprintf(stderr, "Error: Memory allocation failed\n");
        goto cleanup;
    }

    // Simulate reading file content
    if (fread(buffer, 1, 1024, file) == 0) {
        fprintf(stderr, "Error: Failed to read file\n");
        goto cleanup;
    }

    printf("File processed successfully.\n");

cleanup:
    // Cleanup resources
    if (buffer) free(buffer);
    if (file) fclose(file);

    // Return error status
    return (file && buffer) ? 0 : -1;
}

int main() {
    const char *filename = "example.txt";

    if (processFile(filename) != 0) {
        fprintf(stderr, "An error occurred while"
                "processing the file.");
        return 1;
    }

    return 0;
}

Output

Error: Failed to open file 'example.txt'
An error occurred whileprocessing the file.

Limitations of goto in Exception Handling

Though it works fine, goto have some limitations as compared to the specialized exception handling structures.

Overuse can make the code harder to follow especially in larger codebases.
Misuse of goto may lead to bugs or spaghetti code.
Techniques like returning error codes or using modern C libraries (e.g., setjmp and longjmp) can sometimes be better.

Conclusion

While goto is often considered outdated or bad practice, it can be a practical tool for exception handling in C, especially when used judiciously for managing cleanup and errors. By following best practices, such as limiting its scope and keeping the code readable, goto can be a valuable part of a C programmer’s toolkit.

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Article Tags :

Using goto for Exception Handling in C

Why Use goto for Exception Handling?

Examples of goto for Exception Handling

Simulate try-catch Statements

Handling Exception in File Processing

Limitations of goto in Exception Handling

Conclusion

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