Calling C++ Functions in MASM Linker Error

Question

So I am currently trying to run external C++ functions from an assembly program. I have assembly programs running properly, but I keep getting a linker error saying:

"Error LNK2019 unresolved external symbol _testFunc@0 referenced in function __main@0"

I'm wondering why I am getting this error, I assume it's because I'm somehow incorrectly importing my C++ function into my asm program, but I've seen other people do it in a similar way.

Here's my assembly code:

; Created with MASM
.386

.MODEL FLAT, stdcall

.STACK 100h

ExitProcess PROTO, dwExitCode:DWORD

extern testFunc : proto

.CODE
_main PROC

    call testFunc
    xor edi, edi

INVOKE ExitProcess, 0

_main ENDP
END

and my C++ code:

#include <iostream>
using namespace std;

extern "C" void _main();

extern "C" void testFunc()
{
    cout << "Hello world";
}

int main()
{
    _main();

    return 0;
}

Answer 1

You declare .MODEL FLAT, stdcall . You should define the function

extern "C" __stdcall void testFunc()