Finnicky #define behaviour in c++

Question

I've started to follow the Handmade Hero series. He's loading XInput manually, and has therefore created a function stub. It looks like this:

#define X_INPUT_GET_STATE(name) DWORD WINAPI name(DWORD dwUserIndex, XINPUT_STATE *pState)
typedef X_INPUT_GET_STATE(x_input_get_state);
X_INPUT_GET_STATE(XInputGetStateStub) {
    return 0;
}
global_variable x_input_get_state *XInputGetState_ = XInputGetStateStub;
#define XInputGetState XInputGetState_;

This is defined above any other functions. global_variable is a #define of static.

This code very nearly works. It compiles successfully if I use if (XInputGetState_(ControllerIndex, &ControllerState) == ERROR_SUCCESS) but doesn't compile when I use if (XInputGetState(ControllerIndex, &ControllerState) == ERROR_SUCCESS)

However, I can do as follows.

auto func = XInputGetState(ControllerIndex, &ControllerState);
if (func(ControllerIndex, &ControllerState) == ERROR_SUCCESS)

I'm utterly lost as to why this is happening.

You can find the official function definition here

EDIT:

Just to make matters more confusing. The XInputSetState function is also being defined manually.

#define X_INPUT_SET_STATE(name) DWORD WINAPI name(DWORD dwUserIndex, XINPUT_VIBRATION *pVibration)
typedef X_INPUT_SET_STATE(x_input_set_state);
X_INPUT_SET_STATE(XInputSetStateStub) {
    return 0;
}
global_variable x_input_set_state *XInputSetState_ = XInputSetStateStub;
#define XInputSetState XInputSetState_;

I can then call the function like this

XINPUT_VIBRATION Vibration;
Vibration.wLeftMotorSpeed = 60000;
Vibration.wRightMotorSpeed = 60000;
XInputSetState(0, Vibration);

This code runs and compiles without any problems;

Thanks for the help!

That's why you should avoid `#define`, use the C++ language instead — Paul Evans, Dec 25 '15 at 22:30
I realize that there's probably better ways to do this, but I'm following the otherwise amazing series created by Casey Muratori. — Herbstein, Dec 25 '15 at 22:32
You have an extra `;` in `#define XInputGetState XInputGetState_;` — Jarod42, Dec 25 '15 at 22:40
@Jarod42 God freaking dammit. It really is this type of problem that keeps me up at night. How did I not see that?. Thanks for the help! — Herbstein, Dec 25 '15 at 22:41
@Jarod42 I mostly program in C#, so there's some behaviour in c and c++ that seems very strange to me. — Herbstein, Dec 25 '15 at 22:45
Macro are rarely the good solution. Works have been done to reduce their usage (inline methods, constant expressions, template, ...) — Jarod42, Dec 25 '15 at 22:53

Finnicky #define behaviour in c++

0 Answers0