How Can I Reliably Detect the Operating System During C Preprocessor Compilation?

Preprocessor Detection of Operating Systems in C

Detecting the operating system during preprocessor processing is essential for writing cross-platform C/C code. Here's how to achieve this reliably for Mac OS X, iOS, Linux, and Windows:

Most compilers define macros that identify the operating system. For preprocessor detection, these predefined macros are crucial. GCC, for instance, has a comprehensive list, which includes:

</p>
<h1>if defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__NT__)</h1>
<pre class="brush:php;toolbar:false">// Define something for Windows (32-bit and 64-bit)
#ifdef _WIN64
    // Define something unique for Windows (64-bit only)
#else
    // Define something specific for Windows (32-bit only)
#endif

elif APPLE

#include <TargetConditionals.h>
#if TARGET_IPHONE_SIMULATOR
    // iOS, tvOS, or watchOS Simulator
#elif TARGET_OS_MACCATALYST
    // Mac's Catalyst (bridging iOS API into Mac)
#elif TARGET_OS_IPHONE
    // iOS, tvOS, or watchOS device
#elif TARGET_OS_MAC
    // Other Apple platforms
#else
    // Error: Unknown Apple platform
#endif

elif ANDROID

// Handled elsewhere (Android typically conforms to __linux__)

elif linux

// Linux

elif unix

// Unix

elif defined(_POSIX_VERSION)

// POSIX

else

// Error: Unknown compiler

endif

By using these macros, you can reliably detect the operating system during preprocessor processing and tailor your code accordingly, ensuring compatibility across various platforms.

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