Undefined Reference to a function

Question

I\'m using Linux and I have the following files:

main.c, main.h
fileA.c, fileA.h
fileB.cpp, fileB.h

The function F1() is decla

Answer 1

If you're really compiling fileA.c as C, not C++, then you need to make sure that the function has the proper, C-compatible linkage.

You can do this with a special case of the extern keyword. Both at declaration and definition:

extern "C" void F1();
extern "C" void F1() {}

Otherwise the C linker will be looking for a function that only really exists with some mangled C++ name, and an unsupported calling convention. :)

Unfortunately, whilst this is what you have to do in C++, the syntax isn't valid in C. You must make the extern visible only to the C++ code.

So, with some preprocessor magic:

#ifdef __cplusplus
extern "C"
#endif
void F1();

Not entirely pretty, but it's the price you pay for sharing a header between code of two languages.