检查是否函数是用C preprocessor声明？ [英] Check whether function is declared with C preprocessor?

问题描述

是否可以告诉 C preprocessor检查功能（不是宏）是否被声明？我尝试了以下内容，但它不会出现工作

 的#include＆LT;＆stdio.h中GT;INT主要（无效）
{
＃如果定义（printf的）
    的printf（你支持printf \\ n！）;
＃其他
    看跌期权（要么你不支持printf的，或本次测试是行不通的。）;
＃万一
    返回0;
}
 

解决方案

没有。 preprocessor的C编译器和C编译器处理函数声明之前运行。在preprocessor只有那里的文本处理。

然而，大多数的头文件必须包括后卫宏象 _STDIO_H _ ，你可以测试在preprocessor阶段。然而，随着包括后卫宏名称不规范的解决方案是不可移植的。

Is it possible to tell the C preprocessor to check whether a function (not a macro) is declared? I tried the following, but it doesn't appear to work:

#include <stdio.h>

int main(void)
{
#if defined(printf)
    printf("You support printf!\n");
#else
    puts("Either you don't support printf, or this test doesn't work.");
#endif
    return 0;
}

解决方案

No. Preprocessor runs before the C compiler and the C compiler processes function declarations. The preprocessor is only there for text processing.

However, most header files have include guard macros like _STDIO_H_ that you can test for in the preprocessor stage. However, that solution is not portable as the include guard macro names are not standardized.

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