在堆栈上创建的C ++函数返回对象

Question

I know that when I use __stdcall (also true for other calling conventions) the returned value is stored in the eax register. I was wondering how does the following happen:

class MyObject
{
private:
    int fourBytesInt;
    long fourBytesLong;
    char name[256];
};

MyObject ReturnMe()
{
    MyObject myObj = MyObject();

    return myObj;
}

int main(void)
{
    MyObject myObj = ReturnMe();

    return 0;
}

sizeof(myObj) is 264 bytes, how does ReturnMe function can return such a large object since the register can hold 32 bit at max (x86 architecture).

Thanks!

Answer 1

The return value is only placed in the register for data types of small enough size. Otherwise, they are returned as a copy on the stack. Or sometimes the copy can be ellided.