Understanding C++/C Preprocessor
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Preprocessor
#include <stdio.h> includes contents of stdio.h
#error text display text as compile time error
#warning text display text as compile time warning
#pragma compiler specific options
#define M define M
#undef M undefine M
#if (condition) conditional compiling
#ifdef M compiled if M is defined
#ifndef M compiled if M is not defined
#elif (condition) conditional compiling
#else conditional compiling
#endif end conditional section
defined() is macro defined.
!defined() is macro not defined
M ## D combines M and D into MD
#M treat M as string "M"