matlab internal problem and needs to close - reading from dll in MEX

I am working a a project where I have to make a Matlab interface for IR tracking software. (www.free-track.net). FreeTrack provides a SDK in their download with Matlab code which makes a MEX file from C code. The C code reads from a dll called "freetrackClient.dll", which holds the tracking data. When I run FreeTrack and track my head movement, the data of my movement can be seen on the screen.

Now I want to read this data and save it into Matlab. However, when i run the funciton getData, Matlab crashes and says: "MATLAB has encountered a problem and needs to close"

?Why can't i read from the DLL?

[Ken Atwell]

Are you using loadlibrary? Can you add a code fragment (i.e., the MATLAB code you are running that causes the crash)?

[Ezra]

I have the MEX file Freetrack and in Matlab I do

>> Freetrack("getData")

which runs the function "doGetData" in my generated from C, MEX file.

The function "doGetData" checks if there is data the following way:

if (getData(pData)) //call dll function to fill 'data'

{

mexPrintf("Getting data from dll\n");

//copy the returned data into the output variable

mxSetField(plhs[0],0,fieldnames[0], mxCreateDoubleScalar(data.yaw));

mxSetField(plhs[0],0,fieldnames[1], mxCreateDoubleScalar(data.pitch));

mxSetField(plhs[0],0,fieldnames[2], mxCreateDoubleScalar(data.roll));

mxSetField(plhs[0],0,fieldnames[3], mxCreateDoubleScalar(data.x));

mxSetField(plhs[0],0,fieldnames[4], mxCreateDoubleScalar(data.y));

mxSetField(plhs[0],0,fieldnames[5], mxCreateDoubleScalar(data.z));

mxSetField(plhs[0],0,fieldnames[6], mxCreateDoubleScalar(data.dataID));

}

else

{

//display a warning that there was no data

mexPrintf("Nothing returned from FTGetData\n");

}

Answer 1

[Ken Atwell]

Double-check that you've initialized plhs[0] with mxCreateStructArray with at least the seven fields that you reference later one.

When in doubt, start with a working example and modify incrementally from there:

 edit([matlabroot '/extern/examples/mx/mxcreatestructarray.c']);

[Ezra]

Thanks for your comment.

I initialize plhs[0] the following:

const char *fieldnames[] ={"yaw", "pitch", "roll", "x","y","z","dataID"};

plhs[0] = mxCreateStructMatrix(1,1,sizeof(fieldnames)/sizeof(char*), fieldnames);