使用Extern关键字

Question

我熟悉extern关键字，它用于声明存在于其他文件中的变量，但是以下语句是什么意思？

extern "C" const IMAGE_DOS_HEADER __ImageBase;

Answer 1

It means the __ImageBase global variable uses C linkage and that its name should be mangled using the rules for C instead of C++.

EDIT: It just so happens that Raymond Chen recently published an article that demonstrates my original answer was plain wrong: extern "C" does not disable name mangling, it only changes the rules used to perform it. C names can be mangled too.

Answer 2

It means do not mangle the symbol name __ImageBase that follows the extern "C" . In short it ensures you can use the variable in C++ code.

extern "C" specify's the linkage to be applied. In short a Linkage specification.
It tells the C++ compiler to apply linkage of the type of C to the symbol that follows.

Good Read:
Using extern to Specify Linkage
How to mix C and C++