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cozzie

passing FMOD::sound by reference

4 posts in this topic

Hi,

 

I've started to implement FMOD in my game (instead of directsound).

Now I'm struggling with passing a FMOD::Sound as a reference, to my loadsound function.

 

The problem is that the sound isn't loaded at all.

When I replace the pSound parameter 'sound' by a global FMOD::Sound (not passed as parameter), it works fine.

 

What am I overseeing?

 

bool Fmod_LoadSound(char *filename, FMOD::Sound *pSound)
{
	fmodResult = fmodSystem->createSound(filename, FMOD_DEFAULT, 0, &pSound);
	if(!Fmod_ErrorCheck(fmodResult)) return false;

	pSound->setMode(FMOD_LOOP_OFF);
	return true;
}

/**												**
 ** Play a sound through fmod ********************
 **												**/

void Fmod_PlaySound(FMOD::Sound *pSound)
{
	fmodSystem->playSound(FMOD_CHANNEL_FREE, pSound, false, &fmodChannel);
}

In the file where I declare and load the sound:

 

FMOD::Sound	*sound_shoot		= NULL;

	if(!Fmod_LoadSound("data/sound/_shoot.wav", sound_shoot)) return false; 

 

The only thing I found till now is that createSound needs a pointer to a pointer (**FMOD::Sound).

Any help is really appreciated.

Edited by cozzie
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The expression &sound takes the address of the variable sound, which is a parameter to the function and is thus a local variable. If you intend for &sound to reference the sound_shoot pointer, then you need to use a reference or a pointer to the original pointer.

bool Fmod_LoadSound(char *filename, FMOD::Sound *&pSound)
{ ... }
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Thanks, got it working now.

Still struggling a bit in understanding it.

 

If I understand correct I pass a reference to my pointer to the loadsound function, which is then passed as reference to the createSound function.

And if the 'local' sound wasn't a pointer but just: "sound soundshoot" instead of "sound *soundshoot", then it would work with just "*" instead of "&*".

Is this correct?

Edited by cozzie
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The reference is what makes the parameter reference the original object being passed instead of making a local copy.

bool Fmod_LoadSound(char *filename, FMOD::Sound &pSound)
{ ... }
 
FMOD::Sound sound_shoot;
Fmod_LoadSound("data/sound/_shoot.wav", sound_shoot);

 

The asterisk should rather be seen being a part of the type itself than acting as a reference. If you are having troubles wrapping your head around pointers, just wrap them in a typedef and treat them as any other value. Pointers are no different than, say, integers when it comes to being passed as arguments.

typedef FMOD::Sound *fmod_sound_ptr;
 
bool Fmod_LoadSound(char *filename, fmod_sound_ptr &pSound)
{ ... }
 
fmod_sound_ptr sound_shoot;
Fmod_LoadSound("data/sound/_shoot.wav", sound_shoot);

Here, you have a variable of some type, it is being passed by reference to the Fmod_LoadSound object, and you can then get a pointer to the original variable being passed by taking the address of the parameter; &pSound.

 

The fact that it is a pointer and not an object of some class type, or another primitive type, is not relevant. But the pointer is hidden behind a typedef to not confuse the pointer belonging to the original type and the pointer as a result of taking its address.

 

If you want to understand how pointers and references, and pass by pointer and pass by reference, work, then don't learn it with a type that is already a pointer. Just learn it with a regular integer, and progressively change the integer to a typedef:ed custom type, and to a pointer type, and then remove the typedef. This is essentially the core of your problem:

void foo(int v)
{
    v = 42;
}
 
int main()
{
    int v = 0;
    foo(v);
    std::cout << v;
}

Go from here, and gradually replace the integer with other types, and with typedefs, and with pointer types.

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Thanks, that explanation makes it much more clear.

Also the problem I had, I was just passing a copy instead of the reference to the actual sound pointer, no wonder it loaded correcly but didn't play afterwards, sinds loading only happened in the copy and not the 'right' one.

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