宏值的字符串化 [英] Stringification of a macro value

问题描述

我面临一个问题 - 我需要使用宏值同时作为字符串和整数

I faced a problem - I need to use a macro value both as string and as integer.

 #define RECORDS_PER_PAGE 10

 /*... */

 #define REQUEST_RECORDS \
      "SELECT Fields FROM Table WHERE Conditions" \
      " OFFSET %d * " #RECORDS_PER_PAGE \
      " LIMIT " #RECORDS_PER_PAGE ";"

 char result_buffer[RECORDS_PER_PAGE][MAX_RECORD_LEN];

 /* ...and some more uses of RECORDS_PER_PAGE, elsewhere... */

这失败，一个关于流浪＃消息，即使它的工作，我想我会得到的宏名字符串化，而不是值。当然，我可以养活值到最后的方法（LIMIT％D，页* RECORDS_PER_PAGE ），但它既不pretty，也没有效率。
这几次都是这样，当我希望preprocessor没有以特殊的方式对待字符串，将处理它们的内容就像正常的code。
现在，我与 cludged它的#define RECORDS_PER_PAGE_TXT10，但可以理解的，我不开心了。

This fails with a message about "stray #", and even if it worked, I guess I'd get the macro names stringified, not the values. Of course I can feed the values to the final method ( "LIMIT %d ", page*RECORDS_PER_PAGE ) but it's neither pretty nor efficient. It's times like this when I wish the preprocessor didn't treat strings in a special way and would process their content just like normal code. For now, I cludged it with #define RECORDS_PER_PAGE_TXT "10" but understandably, I'm not happy about it.

如何得到它的权利？

推荐答案

下面定义的 XSTR 宏将做宏扩展后的字符串化。

The xstr macro defined below will stringify after doing macro-expansion.

#define xstr(a) str(a)
#define str(a) #a

#define RECORDS_PER_PAGE 10

#define REQUEST_RECORDS \
    "SELECT Fields FROM Table WHERE Conditions" \
    " OFFSET %d * " xstr(RECORDS_PER_PAGE) \
    " LIMIT " xstr(RECORDS_PER_PAGE) ";"

这篇关于宏值的字符串化的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！