Question

Can an extern "C" function accept or return C++-specific data types, such as references, pointers-to-members, or non-POD classes (by value)? I cannot find anything in the C++ standard that forbids this. Logically, I would expect the standard to say something about it, as the C ABI is not necessarily suitable for passing such types around.

The reason for me wanting to use C linkage has nothing to do with C compilers. The function is called only from C++ code. I just want to export unmangled function names from my dynamic libraries.

A silly code example:

class Foo {
  public:
    virtual void doit() = 0;
};

class Bar : public Foo {
  public:
    void doit() { std::cout << "Bar" << std::endl; }
};

extern "C" Foo& getFoo() { static Bar bar; return bar; }

extern "C" Bar getBar() { return Bar(); }

This compiles with GCC on Linux, and works as expected. Should it, standard-wise?

The question is a follow-up to a discussion in the comments to this question.

Update I have tested this with the Comeau compiler, it didn’t complain.

Answer 1

According to section 7.5.9 Linkage specifications (c++11 draft) http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf

“Linkage from C++ to objects defined in other languages and to objects defined in C++ from other languages is implementation-defined and language-dependent. Only where the object layout strategies of two language implementations are similar enough can such linkage be achieved.”