C Conditional Compile

C Conditional Compilation – Preprocessor Directives

Conditional compilation in C allows the compiler to include or exclude parts of the code based on specified conditions. This is particularly useful for creating portable code that can adapt to different environments, configurations, or debugging needs.

🔹 #if, #else, #elif, #endif

The preprocessor directives #if, #else, #elif, and #endif are used to conditionally compile code based on certain conditions or constants.

📝 Example 1: Using #if to Include Code Based on a Condition

The following code will print “Debugging Mode” if the DEBUG constant is defined.

#include <stdio.h>

#define DEBUG

int main() {
    #if defined(DEBUG)
        printf("Debugging Mode\n");
    #else
        printf("Production Mode\n");
    #endif
    return 0;
}

🔹 #elif and #else

You can use #elif for multiple conditions or #else as the default case.

📝 Example 2: Using #elif and #else

This code will check if a specific operating system is defined and print a corresponding message.

#include <stdio.h>

#define LINUX

int main() {
    #if defined(WINDOWS)
        printf("Windows OS\n");
    #elif defined(LINUX)
        printf("Linux OS\n");
    #else
        printf("Unknown OS\n");
    #endif
    return 0;
}

🔹 Nested Conditional Compilation

You can also nest conditional compilation directives inside each other.

📝 Example 3: Nested #if

#include <stdio.h>

#define FEATURE_X

int main() {
    #if defined(FEATURE_X)
        #if defined(DEBUG)
            printf("Feature X in Debug Mode\n");
        #else
            printf("Feature X in Production Mode\n");
        #endif
    #endif
    return 0;
}

⚙️ Common Use Cases

• Enabling or disabling code based on platform or environment (e.g., Windows, Linux).
• Including debugging or logging code only in certain builds.
• Creating cross-platform programs by using conditional compilation for platform-specific code.

🎯 Recap

Conditional compilation is a powerful feature in C that allows you to control which parts of the code are compiled based on conditions defined during preprocessing. It is often used for debugging, cross-platform compatibility, and managing feature sets.