在用C preprocessor条件字符串比较

问题描述

我传递的makefile DPATH 编译器选项调用，这是像 DPATH = /路径/要/ somefile 。基于此，我必须写一个宏这样： -

I am passing a compiler option in makefile called DPATH, which is something like DPATH=/path/to/somefile. Based on this, I have to write a macro such that:-

#if "$(DPATH)"=="/path/to/x"
#error no x allowed
#endif

如何比较 DPATH 在一个preprocessor条件测试字符串？

How do I compare DPATH with the string in a preprocessor conditional test?

推荐答案

这是不可能做到这一点在preprocessor。 ＃如果只能评估整数EX pressions使得没有提及函数或者变量。幸存下来宏扩展所有标识符由零取代，一个字符串常量触发自动语法错误。

It is not possible to do this in the preprocessor. #if can only evaluate integer expressions making no reference to functions or variables. All identifiers that survive macro expansion are replaced by zeroes, and a string constant triggers an automatic syntax error.

不知道更多关于你的问题，我建议写一个编译的一个小的测试程序，并在生成过程中执行的，和Makefile咕失败的构建，如果测试没有通过。

Without knowing more about your problem, I would suggest writing a tiny test program that is compiled and executed during the build, and Makefile goo to fail the build if the test doesn't pass.

#include <stdio.h>
#include <string.h>
int main(void)
{
   if (!strcmp(DPATH, "/path/to/x") || some1 == 3 || some2 == 7 || ...)
   {
       fputs("bogus configuration\n", stderr);
       return 1;
   }
   return 0;
}

然后

all : validate_configuration
validate_configuration: config_validator
    if ./config_validator; then touch validate_configuration; else exit 1; fi
config_validator: config_validator.c
    # etc 

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