Preprocessor

What is preprocessor?

参见:

1、wikipedia Preprocessor

2、microsoft C/C++ preprocessor reference

3、gcc The C Preprocessor

cppreference Preprocessor

The preprocessor is executed at translation phase 4, before the compilation. The result of preprocessing is a single file which is then passed to the actual compiler.

Directives and Capabilities

preprocessing instruction

NOTE: 预编译指令，它们都是以#打头的，下面是对它们的分类

Capabilities	Directive
Conditional inclusion	#if, #ifdef, #ifndef, #else, #elif and #endif
Replacing text macros	1) #define and #undef 2) # and `##
Source file inclusion	include, __has_include(since C++17)
Error directive	error,
Implementation defined behavior control	pragma, _Pragma(since C++11)
Filename and line information	line,

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