gcc 检查文件是否为主文件 (#if __BASE_FILE__ == __FILE__)
在 ruby 中，有一个非常常见的习惯用法来检查当前文件是否是“主”文件：
if __FILE__ == $0
# do something here (usually run unit tests)
end
在阅读 gcc 文档后，我想在 C 中做类似的事情，我认为它应该像这样工作
#if __FILE__ == __BASE_FILE__
// Do stuff
#endif
：唯一的问题是在我尝试这个之后：
$ gcc src/bitmap_index.c -std=c99 -lm && ./a.out
src/bitmap_index.c:173:1: error: token ""src/bitmap_index.c"" is not valid in preprocessor expressions
我使用#if错误吗？
作为未来客人的总结：
- 来比较字符串
- 您不能使用 #if BASE_FILE 是正在编译的文件的名称
- （这实际上是我想要的）。最好的方法是在编译期间使用 -D 设置标志
In ruby there's very common idiom to check if current file is "main" file:
if __FILE__ == $0
# do something here (usually run unit tests)
end
I'd like to do something similar in C after reading gcc documentation I've figured that it should work like this:
#if __FILE__ == __BASE_FILE__
// Do stuff
#endif
the only problem is after I try this:
$ gcc src/bitmap_index.c -std=c99 -lm && ./a.out
src/bitmap_index.c:173:1: error: token ""src/bitmap_index.c"" is not valid in preprocessor expressions
Am I using #if wrong?
As summary for future guests:
- You cannot compare string using #if
- BASE_FILE is the name of file that is being compiled (that Is actually what I wanted).
- Best way to do this is to set flag during compilation with -D
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在 gcc 中，您可以使用：
#if __INCLUDE_LEVEL__ == 0
或：
if(!__INCLUDE_LEVEL__)
来检查您是否在 __BASE_FILE__ 内
in gcc you can use:
#if __INCLUDE_LEVEL__ == 0
or:
if(!__INCLUDE_LEVEL__)
to check if your inside the __BASE_FILE__
是的，您误用了
#if。它仅适用于整数常量表达式。但即使您使用if，比较指针是否相等也绝不是在 C 中比较字符串的有效方法。Yes, you are misusing
#if. It only works on integer constant expressions. But even if you were usingif, comparing pointers for equality is never a valid way to compare strings in C.看来你不能。
或者，它在常规 if 条件下工作得很好，并且 gcc 可以很好地优化它。
但您不能定义新的主函数或使用其他预处理器技巧。但是你可以使用静态方法来短路 main ，但这既严酷又肮脏。
但也许你不应该这样做。在 Ruby/python 中，这是可行的，因为文件的使用是在运行时完成的。在C语言中，所有文件都必须编译才能使用。
请记住，大多数构建系统一次构建一个文件，将它们构建为目标文件，并仅在必要时重建它们。所以
在源文件中大多数时候都会等于（如果不是总是）。我强烈建议您不要在头文件中执行此操作。
将测试放在单独的文件中，仅在需要时链接它们会更容易。
It seems you can't.
Alternatively, it works perfectly fine on a regular if condition, and gcc can optimize this nicely.
but you can't define new main functions or use other preprocessor tricks. but you could short-circuit main by using static methods, but that's harsh and dirty.
But maybe you shouldn't do it. in Ruby/python, this works because usage of files is done at runtime. in C, all files are to be compiled to be used.
Keep in mind that most build system will build one file at a time, building them as object files, and rebuilding them only when necessary. So
will be equals most of the time in sources files, if not always. And i would strongly discourage you to do this in header files.
It's easier to just put your tests in separate files, only linking them when needed.
是的，正如其他人所说，您滥用了它，因为您无法在 C 中以这种方式比较字符串，尤其是在预处理器中。
定义 int main(int argc, char* argv[]) 的文件是主文件。可执行文件中只能有一个这样的函数。
Yup, as others say, you're misusing it since you can't compare strings that way in C, and especially not in the preprocessor.
The file that defines
int main(int argc, char* argv[])is the main file. There can be only one such function in an executable.除了其他人所说的（你不能让 C 预处理器比较字符串）之外，请小心
__BASE_FILE__因为它可能与你对“主”文件的定义不对应。__BASE_FILE__是正在编译的文件的名称，因此它始终等于源文件中的__FILE__，仅在头文件和其他包含的文件中有所不同。特别是，
__BASE_FILE__不是包含main()函数的文件的名称。In addition to what others have said (you can't have the C preprocessor compare strings), be careful with
__BASE_FILE__because it may not correspond to your definition of "main" file.__BASE_FILE__is the name of the file being compiled, so it's always equal to__FILE__in source files, and only differs in headers and other included files.In particular,
__BASE_FILE__is not the name of the file which contains themain()function.