#include "stdafx.h"
#include <Windows.h>
extern "C" void hello(); //THIS IS OK
class vector4
{
public:
    vector4(){hello();}
    extern "C" void  asm_proc(); //HERE IT THROWS AN ERROR
};

int _tmain(int argc, _TCHAR* argv[])
{
    hello();
    char buffer[256];
    vector4 vv;
    vv.asm_proc();
    int x=10+2;
    return 0;
}

.code
hello proc
    mov rax,234
    add rax,10
    ret
hello endp
asm_proc proc
    mov rax,0
    ret
asm_proc endp
end