Why would you use 'extern “C++”'?

Question

In this article the keyword extern can be followed by \"C\" or \"C++\". Why would you use \'extern \"C++\"\'? Is it practical?

Answer 1

extern "C" is used to say that a C++ function should have C linkage. What this means is implementation dependant, but normally it turns off C++ name-mangling (and so overloading and strict type checking). You use it when you have a C++ function you want to be called from C code:

extern "C" void Foo();   // can be called easily from C

As for extern "C++", I've never seen it in real code, though the C++ Standard allows it. I guess it is a no-op.