C 编程/预处理器参考

预处理器参考

存在以下预处理器语句

Statement Subsequent items on the control line Meaning
========= ==================================== =======
#if       conditional-expression               conditional
#ifdef    identifier                           true iff identifier is a macro
#ifndef   identifier                           true iff identifier is not a macro
#elif     conditional-expression               continues a conditional
#else                                          continues a conditional
#endif                                         ends a conditional
#include  header-name                          includes a file
#define   identifier                           defines a macro
#undef    identifier                           removes a previously defined macro
#line     number filename                      changes the line number and file name
#error    token-list                           specifies an error
#pragma   token-list                           catchall

一些非标准编译器也指定#warning和#import.

上面的条件表达式可以包含定义运算符。

上面的#define 标识符后面可以跟可选的参数列表，然后是可选的替换标记列表。参数列表的左括号必须没有前导空格。