goto statement in C ? with example

 

goto statement in C

The goto statement is known as jump statement in C. As the name suggests, goto is used to transfer the program control to a predefined label. The goto statment can be used to repeat some part of the code for a particular condition. It can also be used to break the multiple loops which can't be done by using a single break statement. However, using goto is avoided these days since it makes the program less readable and complecated.

Here's the basic syntax of the goto statement:

c
label_name:
// Code here

// Somewhere else in your code
goto label_name; // This will transfer control to the labeled part of the code

Flowchart of goto statement in C

goto example

Here's a simple example of how you might use goto:

c
#include <stdio.h>

int main() {
    int i = 0;

loop_start:
    if (i < 5) {
        printf("%d\n", i);
        i++;
        goto loop_start; // Jump back to the 'loop_start' label
    }

    return 0;
}

When should we use goto?

The only condition in which using goto is preferable is when we need to break the multiple loops using a single statement at the same time.

1. Error handling and resource cleanup in C:

   In C programming, where you don't have exceptions like in some other languages, goto can be used for error handling and resource cleanup in situations where you have multiple points that need to be cleaned up before returning from a function. For example:

   c
   FILE *file = fopen("example.txt", "r");
   if (file == NULL) {
       goto cleanup;
   }
   
   // Code to read the file
   
   cleanup:
       if (file != NULL) {
           fclose(file);
       }

   This pattern ensures that the file is closed before exiting the function, even if there are multiple early exit points due to errors.

2. Breaking out of nested loops:

   Sometimes, in nested loops, you may want to break out of multiple levels of loops at once. In such cases, goto can be used to transfer control to a label outside of the nested loops. This is often seen as a less elegant alternative to using flags or restructuring your code, but it can be necessary in certain situations.

   c
   for (int i = 0; i < 10; i++) {
       for (int j = 0; j < 10; j++) {
           if (some_condition(i, j)) {
               goto exit_loops;
           }
       }
   }
   
   exit_loops:
   // Code here will be executed after breaking out of the nested loops

3. Low-level code and embedded systems:In some low-level programming scenarios, such as writing code for embedded systems or dealing with hardware interfaces, goto might be used to implement state machines or handle exceptional conditions. In such cases, it is important to use goto judiciously and document the reasons for its use clearly.

4. Code generated by automated tools:Occasionally, automated code generation tools might produce code that includes goto statements as part of their output. In such cases, you may not have control over the generated code, and you may need to work with the goto statements as they are.