Returning error number as string when only Int32Ptr is accepted in Matlab

I'm new to using dll files in Matlab and am having some trouble returning the errorNumber and the value of xMotor. The documentation for the dll is specific to C and suggests using the following to achieve what I want to:

#include “PiUsb.h”
void * pUsb1;
int ErrorNumber;
int MotorSerialNumber = 10; // Serial number from Motor

pUsb1 = piConnectMotor(&ErrorNumber,MotorSerialNum);
if (ErrorNumber == PI_DEVICE_NOT_FOUND)
AfxMessageBox( "Unable to find Motor..." );
else
AfxMessageBox( "Motor Connected." );

However, I want to be able to do this in Matlab.

I've succesffully loaded the dll into Matlab with:

fullpathToPiUSBHeader = [pwd filesep 'picardStage' filesep 'PiUsb.h']
fullpathToPiUSBDll = [pwd filesep 'picardStage' filesep 'PiUsb.dll']
fullpathToPiUSBHeader = [pwd filesep 'picardStage' filesep 'PiUsb.h']

if not(libisloaded(fullpathToPiUSBHeader))
  loadlibrary(fullpathToPiUSBDll,fullpathToPiUSBHeader)
end

libfunctions('PiUsb','-full')

And I'm returned the full list of functions, in particular this function:

[lib.pointer, int32Ptr] = piConnectMotor(int32Ptr, int32)

This is what I've got so far:

errorNumber = libpointer('int32Ptr',0);
xMotor = libpointer('voidPtr');
xMotor = calllib('PiUsb','piConnectMotor',errorNumber,xMotorSerialNumber)

I want to be able to get the errorNumber result back as well as the value for xMotor, however their values are just returned as "libpointer". Any ideas on how I can access the values/results?

Any help would be greatly appreciated!

Answer 1

[Philip Borghesani]

Remember that MATLAB creates everything(*) on the left of an equals sign and don't bother initializing xMotor and errorNumber then call:

[xMotor,errNumber] = calllib('PiUsb','piConnectMotor',0,xMotorSerialNumber);

errNumber should contain an integer value and xMotor will contain an unreadable handle (void*) that can be passed to other functions.

In your code errorNumber should have had a value what is

errorNumber.value

*Provided no indexing is done on the LHS