bool CALLBACK EnumJoysticksCallback(DIDEVICEINSTANCE* pdidInstance, VOID* pContext);
m_lpDI->EnumDevices(DI8DEVCLASS_GAMECTRL,&DX_INPUT::EnumJoysticksCallback ,NULL,DIEDFL_ATTACHEDONLY)
[C++] Pointer to member problem
Author
I'm following the directInput tutorial to setup joystick input and I'm stuck at one part.
I have the direct input class (called DX_INPUT). In this class I have a function:
I have to pass this function as a parameter here:
I've gone through some tutorials on pointer to memeber functions but I still can't get it to work.
I get this error:
Error 1 error C2664: 'IDirectInput8W::EnumDevices' : cannot convert parameter 2 from 'bool (__stdcall DX_INPUT::* )(DIDEVICEINSTANCE *,void *)' to 'LPDIENUMDEVICESCALLBACKW'
help would be very appreciated :D
A member function pointer is not the same thing as a function pointer, which is what DIEnumDevicesCallback expects.
Edit: Also, I'm pretty sure return type is taken as part of the pointer to function type, in which case
bool (*)(DIDEVICEINSTANCE*, VOID*) is not a
BOOL (*)(DIDEVICEINSTANCE*, VOID*)
Edit: Also, I'm pretty sure return type is taken as part of the pointer to function type, in which case
bool (*)(DIDEVICEINSTANCE*, VOID*) is not a
BOOL (*)(DIDEVICEINSTANCE*, VOID*)
Quote:Original post by Driv3MeFar
A member function pointer is not the same thing as a function pointer, which is what DIEnumDevicesCallback expects.
Edit: Also, I'm pretty sure return type is taken as part of the pointer to function type, in which case
bool (*)(DIDEVICEINSTANCE*, VOID*) is not a
BOOL (*)(DIDEVICEINSTANCE*, VOID*)
You are correct, however that probably gets by the compile since it can implicitly cast it.
Author
thx for the help so far but I still can't figure it out...
this is a part of the .h file that defines the CALLBACK function:
this is a part of the .cpp file:
can someone tell me what exactly do I need to change to get this working??
this is a part of the .h file that defines the CALLBACK function:
class DX_INPUT{...... // Callback function BOOL CALLBACK EnumJoysticksCallback(DIDEVICEINSTANCE *pdidInstance, void *pContext);...... };this is a part of the .cpp file:
........// The callback functionBOOL DX_INPUT::EnumJoysticksCallback(DIDEVICEINSTANCE *pdidInstance, void *pContext){ // Obtain the interface to the enumerated joystick if(FAILED (m_lpDI->CreateDevice(pdidInstance->guidInstance,&m_pJoystick,NULL) )) { ONMESSAGE("cannont obtain joystick intefaces","error:dxinput"); return DIENUM_STOP; } return DIENUM_CONTINUE;}// In this function the EnumJoysticksCallback is passed as an paramter for m_lpDI->EnumDevices:void DX_INPUT::InitializeJoysticks(){ m_lpDI->EnumDevices(DI8DEVCLASS_GAMECTRL, !CALLBACK_FUNCTION_GOES_HERE! ,NULL,DIEDFL_ATTACHEDONLY)}can someone tell me what exactly do I need to change to get this working??
as Dave said: Make the function a static member:
static BOOL CALLBACK EnumJoysticksCallback(DIDEVICEINSTANCE *pdidInstance, void *pContext);
static BOOL CALLBACK EnumJoysticksCallback(DIDEVICEINSTANCE *pdidInstance, void *pContext);
Quote:Original post by n3XusYou can't pass a non-static function to a callback like that, so you need to make the function static. A member function has an implicit "this" pointer, which means that it's not the same as a free-standing function, so you can't pass it in as a function pointer.
thx for the help so far but I still can't figure it out...
this is a part of the .h file that defines the CALLBACK function:
*** Source Snippet Removed ***
this is a part of the .cpp file:
*** Source Snippet Removed ***
can someone tell me what exactly do I need to change to get this working??
Doing that means that you can't access any member variables from within the function though, since it doesn't have a "this" pointer. That's what the context parameter is for.
You want the following...
Header:
static BOOL CALLBACK EnumJoysticksCallback(DIDEVICEINSTANCE *pdidInstance, void *pContext);
Source file:
// The callback functionBOOL DX_INPUT::EnumJoysticksCallback(DIDEVICEINSTANCE *pdidInstance, void *pContext){ DX_INPUT* pThis = (DX_INPUT*)pContext; // Obtain the interface to the enumerated joystick if(FAILED (pThis->m_lpDI->CreateDevice(pdidInstance->guidInstance, pThis->&m_pJoystick, NULL) )) { ONMESSAGE("cannont obtain joystick intefaces","error:dxinput"); return DIENUM_STOP; } return DIENUM_CONTINUE;}// In this function the EnumJoysticksCallback is passed as an paramter for m_lpDI->EnumDevices:void DX_INPUT::InitializeJoysticks(){ m_lpDI->EnumDevices(DI8DEVCLASS_GAMECTRL, EnumJoysticksCallback, this, DIEDFL_ATTACHEDONLY)}That way, you pass in the "this" pointer as the context parameter to the callback function, then you grab it out and use it.
Author
thx Steve, I saw that "this passing" in a tutorial but I didn't know I can use VOID* pContext to pass it :D
Quote:Original post by n3XusYeah, it's fairly standard that any C-style callback function like this will take a void* "user context" parameter that you can use to communicate with the function. There's some exceptions of course, but every Win32 and DirectX callback I can think of allows this.
thx Steve, I saw that "this passing" in a tutorial but I didn't know I can use VOID* pContext to pass it :D
<offtopic>
Quote:Original post by DaveI'm slow today - I'm ball deep in code at work [sad]
Cue Evil Steve....
[BAM]
P.S: Make the function a static member.
</offtopic>
Author
damnit it still doesn't work :@ I'm gonna have nightmares because of this thing.
Now the problem is if I write:
m_lpDI->EnumDevices(DI8DEVCLASS_GAMECTRL, EnumJoysticksCallback ,this,DIEDFL_ATTACHEDONLY)
I get this error:
Error 1 error C2664: 'IDirectInput8W::EnumDevices' : cannot convert parameter 2 from 'BOOL (__stdcall *)(DIDEVICEINSTANCE *,void *)' to 'LPDIENUMDEVICESCALLBACKW'
If I write it like this:
m_lpDI->EnumDevices(DI8DEVCLASS_GAMECTRL, (LPDIENUMDEVICESCALLBACKW)EnumJoysticksCallback ,this,DIEDFL_ATTACHEDONLY)
it compiles but the function doesn't get exectuted (m_pJoystick remains NULL and I also put a Beep(,) in it and it doesn't beep. So yet again I ask for your assistance
Now the problem is if I write:
m_lpDI->EnumDevices(DI8DEVCLASS_GAMECTRL, EnumJoysticksCallback ,this,DIEDFL_ATTACHEDONLY)
I get this error:
Error 1 error C2664: 'IDirectInput8W::EnumDevices' : cannot convert parameter 2 from 'BOOL (__stdcall *)(DIDEVICEINSTANCE *,void *)' to 'LPDIENUMDEVICESCALLBACKW'
If I write it like this:
m_lpDI->EnumDevices(DI8DEVCLASS_GAMECTRL, (LPDIENUMDEVICESCALLBACKW)EnumJoysticksCallback ,this,DIEDFL_ATTACHEDONLY)
it compiles but the function doesn't get exectuted (m_pJoystick remains NULL and I also put a Beep(,) in it and it doesn't beep. So yet again I ask for your assistance
This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
