函数的C ++ extern关键字。为什么不包括头文件？ [英] C++ extern keyword on functions. Why no just include the header file?

问题描述

如果我理解正确，这意味着

If I understand it correctly this means

extern void foo();

函数foo在另一个翻译单元中声明。

that the function foo is declared in another translation unit.

1）为什么不只是#include标题中声明这个函数？

1) Why not just #include the header in which this function is declared?

2）链接器如何知道在链接时间？

2) How does the linker know where to look for function at linking time?

编辑：也许我应该澄清上面的声明，然后使用函数

edit: Maybe I should clarify that the above declaration is then followed by using the function

foo();

在此翻译单元中未定义。

It is never defined in this translation unit.

推荐答案

1）它可能没有头文件。但是，一般来说，对于大型项目，如果有多个翻译单元要使用该函数，您应该有一个头文件（不要重复自己）。

1) It may not have a header file. But yes, in general, for large projects, you should have a header file if multiple translation units are going to use that function (don't repeat yourself).

2 ）链接器搜索所有被告知要找到函数和其他符号的对象文件和库。

2) The linker searches through all the object files and libraries it was told about to find functions and other symbols.

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