How to pass two arguments and their size to a C-function?

I have to call the following C-library function out of Matlab:

bool PI_OAD (int ID, const int* channel, const double* pdValueArray, int iArraySize)

and the parameter iArraySize should be the size of the arrays channel and pdValueArray.

The parameters channel and pdValueArray are given as follows:

pChannel = uint8(channel);
pStep = uint16(step);

And my calllib command is:

calllib(Controller, 'PI_OAD', ID, pChannel, pStep, int32(24));

It doesn't work.

I don't know how to pass the size of the parameters channel and step correctly. Does somebody have an idea?? Thanks!