Returned Data query

**ozzy34** · 06-23-2004

Hi guys

I'm a c++ newbie and am having issues with returned data.

In the documentation of the toolkit I'm using I'm provided with the following method:

SbBool SoVolumeData::getVolumeData ( SbVec3s & dimension,
void *& data, SoVolumeData:: DataType & type, int * numSignificantBits = NULL
)

Im trying to use the following code to get info pulled back but cant get this to work:

Code:

SoVolumeData *volData = new SoVolumeData();
volData->fileName.setValue("./Data/WORSLEY-MAN.am");
SbVec3s volDims = NULL;
SoVolumeData *ptoData;
SoVolumeData::DataType dtype ;
int sigBits =0;
volData->getVolumeData(volDims, ptoData, dtype, sigBits);

Upon compiling I get the following error msg:

error C2664: 'getVolumeData' : cannot convert parameter 2 from 'class SoVolumeData *' to 'void *& '
A reference that is not to 'const' cannot be bound to a non-lvalue

Any ideas what I need to alter in my code to resolve this...

Thanks

**Prelude** · 06-23-2004

That's interesting. You don't see void pointers used much in C++. Anyway, the problem is that the pointer-to-T to pointer-to-void conversion results in an rvalue. You can't have a reference to an rvalue, so the function call is ill-formed. It also means that an explicit cast is also not going to work for the same reason.

The only way I can think of at the moment to work around this particular problem without changing the parameter list of the function in question is to use a void pointer first, then point ptoData to it after the function call:

Code:

void *vptoData;
volData->getVolumeData(volDims, vptoData, dtype, sigBits);
SoVolumeData *ptoData = static_cast<SoVolumeData*>(vptoData);

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