c++ - 如何避免cpp给宏参数加空格

Question

我公司有 1000 多个使用宏指定包含路径的源文件。我无法更改它，它适用于当前的编译器。现在，我尝试用 GCC(4.8.2 或 3.4.6)编译它，但它失败了。

基本上有这样一个宏:

#define COMP_INC(comp, file) <comp/include/file>

就是这样使用的:

#include COMP_INC(posix, inttypes.h)

我的问题是 GCC 出于某种未知原因将我的宏调用转换为:

#include <posix/include/ inttypes.h>

注意到“inttypes.h”之前的空格了吗？因此，找不到头文件。

为什么预处理器要插入一个空格？我可以避免吗？我只能更改宏，不能更改使用它的源文件。

Answer 1

删除 posix 和 inttypes.h 之间的空格(逗号后)。问题消失了。

这answer告诉我们为什么会这样:

From the C99 standard:

A preprocessing directive of the form

# define identifier replacement-list new-line

defines an object-like macro that causes each subsequent instance of the macro name to be replaced by the replacement list of preprocessing tokens that constitute the remainder of the directive.

---

So macros work on tokens and the whitepace is to be expected.

编辑:

根据这个answer ，您可以使用 traditional-cpp 标志来模仿不添加空格的旧行为。我不确定这将如何影响您的构建，但您可以尝试一下:

Only much older preprocessors didn't insert that extra space -- note that original entry was submitted over 20 years ago in 1988, before the 1989 version of the C standard was standardized. You can pass the -traditional-cpp flag to the GCC preprocessor, which causes it to imitate the behavior of old-fashioned C preprocessors, as opposed to ISO C preprocessors.