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4.11 The C Preprocessor C预处理器
C provides certain language facilities by means of a preprocessor, which is conceptionally a separate first step in compilation. The two most frequently used features are #include, to include the contents of a file during compilation, and #define, to replace a token by an arbitrary sequence of characters. Other features described in this section include conditional compilation and macros with arguments.
C语言通过预处理器提供了一些语言功能。从概念上讲，预处理器是编译过程中单独执行的第一个步骤。两个最常用的预处理器指令是：#include指令(用于在编译期间把指定文件的内容包含进当前文件中)和#define指令(用任意字符序列替代一个标记)。本节还将介绍预处理器的其他一些特性，如条件编译与带参数的宏。