MATLAB: Mex crashes when adding input AND calling function

crashMATLABmex

My mex file crashes only when I provide an input AND call a function. I'm having a hard time figuring out what is actually going on. Here is a shortened version of the code that reproduces the behavior.
Definitions of the library I am calling can be found at:
https://github.com/JimHokanson/adinstruments_sdk_matlab/blob/master/ADIDatCAPI_mex.h
I can include them here if it turns out to be relevant.
Code from void mex
    double *option;
    long *nRecords;
    int *x, *y;
    int file_handle_value;
    wchar_t *path = L"MY_PATH";
    ADIResultCode result;
    ADI_FileHandle fileH(0); //Pointer to ADI_FileHandle__
    option = mxGetPr(prhs[0]);
        result = ADI_OpenFile(path, &fileH, kOpenFileForReadOnly);
        //printf("Result: [s[%d]]
        //printf("Result: %x\n",result);
        if (result == 0)
        {
            printf("unused: %d\n",fileH->unused);
            //Size 4 - not sure if this will change to 8 ...
            //Might need to have a check ...
            //printf("pointer size: %d\n",sizeof(fileH));
            printf("pointer_value: %d\n",fileH);
        }
        //Uncommenting this call crashes Matlab, but only if option line is uncommented as well
        //result = ADI_GetNumberOfRecords(fileH,nRecords);
Call line:
sdk_test(0) %Name of the mex file
Crashes when option AND second result are both uncommented, but not one or the other

Best Answer

The problem goes away when I predefine nRecords and change it from a pointer to a value.
What's not clear to me is why the crash happens only after I start working with inputs (outputs too??) in the mex entry function.
So instead of:
long *nRecords;
result = ADI_GetNumberOfRecords(fileH,nRecords)
I do:
long nRecords;
result = ADI_GetNumberOfRecords(fileH,&nRecords)
This in general is probably good practice???; especially when passing values to a 3rd party library.
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