是应该的#define周围添加宏空间？ [英] Is #define supposed to add spaces around macros?

问题描述

我在 http://www0.us.ioccc.org看节目/1988/westley.c ，在另一SO回答 - 它应该打印PI，约3.142的价值，但是当我编译并运行它，我得到 0.250 。它看起来当GCC preprocessor（包括4.1.2和3.4.6测试）在code运行状，将其转换

I was looking at the program at http://www0.us.ioccc.org/1988/westley.c, mentioned in another SO answer - it's supposed to print the value of pi, about 3.142, but when I compile it and run it I get 0.250. It looks like when the GCC preprocessor (both 4.1.2 and 3.4.6 tested) runs on the code, it converts

#define _ -F<00||--F-OO--;
_-_-_

到

-F<00||--F-OO--;- -F<00||--F-OO--;- -F<00||--F-OO--;

但我认为，该计划的工作，它应该是

but I think, for the program to work, it should be

-F<00||--F-OO--;--F<00||--F-OO--;--F<00||--F-OO--;

即。 GCC被插入的宏扩张之前额外的空间。是的方式的#define 应该工作？ （有自1988年以来改变了吗？）

i.e. GCC is inserting an extra space before the "macro" expansion. Is that the way #define is supposed to work? (Has that changed since 1988?)

的修改的。此外，有关如何prevent任何信息的空间无法显示了将AP preciated

EDIT: Also, any information about how to prevent those spaces from showing up would be appreciated.

推荐答案

在preprocessor令牌上操作，没有严格的文本。因此从技术上讲并不把空间之间，但除非你明确告诉它两个标记与 ## 运营商贴在一起，它不会做。在这种情况下，两个 - 的整个宏观行被视为两个不同的标记 - 既意味着一元减，不减少

The preprocessor operates on tokens, not strictly text. So technically it doesn't "put a space" in between, but unless you explicitly tell it to paste two tokens together with the ## operator, it won't do it. In this case the two -'s across macro lines are counted as two different tokens - both meaning unary minus, not decrement.

另见： http://en.wikipedia.org/wiki/C_ $ p $＃pprocessor ​​ Token_concatenation

see also: http://en.wikipedia.org/wiki/C_preprocessor#Token_concatenation

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