The C programming language [book]

Cosmomi123456

于 2018-05-23 17:45:00 发布

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原文链接：http://www.cnblogs.com/youchihwang/p/9078105.html

本文深入探讨了C/C++预处理器中的宏定义机制，详细解释了如何使用#define指令定义宏，以及当对同一标识符进行二次#define时可能遇到的问题。文章通过示例展示了错误的宏重新定义将引发警告信息。

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A12.3 Macro Definition and Expansion

A control line of the form
#define identifier token-sequence
causes the preprocessor to replace subsequent instances of the identifier with the given
sequence of tokens; leading and trailing white space around the token sequence is dis-
carded. A second #define for the same identifier is erroneous unless the second token
sequence is identical to the first, where all white space separations are taken to be
equivalent

這段其中有一個小段，我看了許久才知道作者想要表達什麼，
A second #define for the same identifier is erroneous unless the second token
sequence is identical to the first

#define A 123
#define A 1234 <<<==== warning message

转载于:https://www.cnblogs.com/youchihwang/p/9078105.html