Weird void** ?

[codegurugeek]

Guys,

i don't know what is the difference between "void**" and "void"??
I even look through the msdn webside with that keyword.. but couldn't get any result...
Can anyone explain to me ?

[SouthernCodeMonkey]

See MSDN:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccelng/htm/key_s-z_9.asp

Regards.

[codegurugeek]

alright.. base on the explanation from the msdn.. i understand that if

void --> for function usage;
void* --> universal pointer;
void** --> ?

is void ** = &(void*)??

[SouthernCodeMonkey]

Yes, void** is ptr to void ptr.

[NoHero]

void = Nothing. Not even for function declaration that do not return something...

// A function that has no arguments
int main ( void )
{
return 0;
}

You can even cast something to void:

// Cast to void, to tell the compiler to make an optimation for not checking and/or storing the return value
int main ( void )
{
(void)printf("Hello World\n");
return 0;
}

void* ... Is an universal pointer that does not need casting in C but so in C++.
void** ... A pointer to a pointer. (A string array for example). Since void is nothing special at all you cannot use the [] operators to declare an array of pointers. So void * narf[] is not allowed because it is of an unspecified type of size. But for example char* narf[] would be allowed because the size of char is specified. To avoid this problem you write void ** which would be the same as void *[] if it would be allowed.

[codegurugeek]

Alright.. got it..

However, why isnt the one below working?

IGraphBuilder* igb;
IMediaControl* imc;

void* tempimc = imc;
temphr = igb->QueryInterface(IID_IMediaControl,&tempimc);

i am getting the annoying error
Stating that i "can't convert * __gc* to void**"

may i know what is the matter?

[NoHero]

IGraphBuilder* igb;
IMediaControl* imc;

void* tempimc = imc;
temphr = igb->QueryInterface(IID_IMediaControl,&tempimc);

The compiler thinks those two pointers are managed pointers, but are in fact only unmanaged COM pointers. Use __nogc to mark non-managed pointers.