When is "extern C " necessary in c++ in windows?

Question

As we know that we can use c functions directly in c++, when is extern "C" necessary then?

Answer 1

If your function is implemented in a .c file, the .cpp files will need the extern "C" reference, or else they'd reference a mangled C++-style function name, and the link would fail.

It's also handy for exporting functions from DLLs so that they are exported with a non-mangled name.

Answer 2

It's necessary when a C++ function must be called by C code rather than C++ code.

Basically, when you want your C++ library to be backwards compatible.