C #error

In C, the #error directive is a preprocessor directive that allows you to generate a compilation error with a custom error message at compile time. This can be useful for providing developers with specific information or preventing the code from being compiled under certain conditions.

Here’s the basic syntax of the #error directive:

#error error_message

• error_message is the custom error message that you want to display when the #error directive is encountered during compilation.

Here’s an example of how to use #error:

#include <stdio.h>

#ifndef DEBUG
    #error "DEBUG flag is not defined. Please define DEBUG to enable debugging."
#endif

int main() {
    // Your program code here
    return 0;
}

In this example, the program uses #ifndef (if not defined) to check if the DEBUG flag is defined. If it’s not defined, the #error directive is triggered, and the custom error message is displayed during compilation.

When you attempt to compile this program without defining the DEBUG flag, you will see the error message:

#error "DEBUG flag is not defined. Please define DEBUG to enable debugging."

To resolve the error, you can define the DEBUG flag when compiling:

gcc -DDEBUG program.c -o program

By defining the DEBUG flag using the -D compiler option, you enable debugging in your code and prevent the #error directive from triggering.