#error in C

The #error directive in C is used to generate a custom error message during compilation.

When the compiler encounters #error, it halts the compilation process and displays the specified error message.

This directive is helpful for enforcing certain conditions or constraints at compile-time and aiding in code debugging and validation.

Syntax of #error in C

#error "error_message"

Example:

 // Program for #error in C
#include<stdio.h> 

#ifndef CONFIG_ENABLED
#error "CONFIG_ENABLED is not defined. Please define it before compiling."
#endif

int main() {
    printf("Program is running.\n");
    return 0;
}

Output:

If you try to compile the above code without defining CONFIG_ENABLED, you will get the following error message:

#error "CONFIG_ENABLED is not defined. Please define it before compiling."

The compilation process will be halted, and the specified error message will be displayed, indicating that CONFIG_ENABLED needs to be defined before compiling.

Uses of #error in C

Configuration Checks: To ensure that certain configurations or macros are defined before compiling the code.

#ifndef FEATURE_X
#error "FEATURE_X is required for this code."
#endif

Platform Requirements: To enforce platform-specific requirements or constraints.

#ifndef _WIN32
#error "This code requires a Windows platform."
#endif

Debugging: To provide specific error messages that help in debugging or understanding the requirements of the code.

#ifndef DEBUG_LEVEL
#error "DEBUG_LEVEL is not defined. Please specify the debug level."
#endif

The #error directive is a powerful tool for enforcing conditions at compile-time, ensuring that certain requirements are met before proceeding with the compilation, and providing informative error messages to assist in debugging and validation.