#error in C

In C Language, the #error directive is a preprocessor directive that allows us to generate a compilation error with a custom error message.

It is useful for ensuring that certain conditions or requirements are met during compilation.

When an error is encountered, the `#error` directive halts the compilation process and displays the specified error message.

The `#error` directive is typically used within conditional compilation directives such as #ifdef, #ifndef, #if, #elif, #else.

Syntax:

#error error_message

Where "error_message" is the custom error message that we can display when the directive is encountered during preprocessing.

Missing Required Macro:

Example:

#include <stdio.h>

#ifndef MAX_SIZE
#error "MAX_SIZE macro is not defined. Please define MAX_SIZE before compiling."
#endif

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

Output:

#error "MAX_SIZE macro is not defined. Please define MAX_SIZE before compiling.

the program checks if the MAX_SIZE macro is defined.
If it is not defined, the #error directive is triggered, causing the compilation to fail with the specified error message: "MAX_SIZE macro is not defined.
Please define MAX_SIZE before compiling."

Incorrect Compiler Version

Example:

#if __GNUC__ < 13
#error "This program requires GCC version 13 or higher."
#endif

#include <stdio.h>

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

Output:

#error This program requires GCC version 13 or higher.

the program checks if the compiler's version supports the 13 or higher.
If it doesn't (as indicated by the value of __GNUC__), the #error directive is triggered, displaying the error `This program requires GCC version 13 or higher.`.

Platform-specific Compilation:

Example:

#include <stdio.h>

#ifndef __linux__
    #error "This program will not compiled on non Linux system."
#endif

int main() {
    printf("Hello, Linux!\n");
    return 0;
}

The `#error` directive ensures the program is compiled only on a Linux system.
If the `__linux__` macro is not defined (indicating compilation on a non-Linux system), the compilation process halts with the specified error message.

Output:

 #error "This program will not compiled on non Linux system."

Note:

These examples demonstrate how "#error" can be used to enforce specific conditions or requirements during the compilation process, ensuring that the program is compiled under the desired constraints.

<-- #undef