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Please enable JavaScript in your browser settings or update your browser.Вивчайте Fundamentals of Conditional Compilation | Conditional compilation
C Preprocessing
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C Preprocessing

C Preprocessing

1. Introduction to Preprocessing
Introduction to Compilation StagesRole of the PreprocessorPreprocessing Commands
2. Macros
Symbolic ConstantMacro With ArgumentsAdvanced Usage of Symbolic ConstantCancel MacroStringify Operators
3. Conditional compilation
Fundamentals of Conditional CompilationPitfalls and Best Practices

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Fundamentals of Conditional Compilation

It does not affect the runtime behavior but determines what gets into the final binary.

This is useful for adapting code for different platforms, configurations, or versions.

Tipical use cases include:

  • Debug builds: iIserting logs only during development;

  • Platform-specific code: Use #ifdef _WIN32 for Windows, __linux__ for linux;

  • Feature toggling: Enabling or disabling modules based on cofiguration (e.g., Bluetooth support).

The preprocessor evaluates conditions based on defined macros.

Expressions in #if and #elif are evaluated similarly to C expressions but with limited operators (arithmetic, logical, comparison).

c

main

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#include <stdio.h>
#define FEATURE_ENABLED

int main() {
#ifdef FEATURE_ENABLED
    printf("Feature is active!\n");
#endif
    return 0;
}

This code prints the message only if FEATURE_ENABLED is defined. If not, the line is completely removed before compilation.

Multiple conditional branches example:

c

main

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#include <stdio.h>
#define VERSION ___ // choose 1, 2 or another value

int main() {
    #if VERSION == 1
        printf("Old version\n");
    #elif VERSION == 2
        printf("Current version\n");
    #else
        printf("Unknown version\n");
    #endif
    return 0;
}

This code is similar to a switch...case statement or an if() statement. However, the main difference is that the branching happens before the program actually starts running, because swithc...case and if() work at runtime.

question mark

What is the purpose of conditional compilation in C?

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