CODEWITHSUNDEEP
c++mat-file
marcman
marcman

Reputation: 3391

Writing MAT files: Access violation writing location after 508 successful calls

I'm running a 64-bit C++ program in VS2012 that processes images and writes the results to a MAT file. For whatever reason, after 508 working iterations, I get:

"Unhandled exception at ____ (libmat.dll) in Program.exe:____. Access violation writing location ____." (Underscores represent address locations)

However, if I restart the program on image number 509 (changing nothing else; just a restart), it works just fine for the next 508 images and then hands me the same error again.

A comment on an earlier, less-detailed post said it may be some memory issue. Perhaps I'm not handling garbage collection properly? I can't figure it out though.

For the record, all of the data being saved to files ends up in a 127x47 (row x col) double matrix. That means each of the 508 successful files contained 5969 doubles (plus whatever metadata goes into a MAT file). Perhaps some memory limit gets reached because I don't clear it properly?

The code in question is below:

void writeMat (void * data, int rows, int cols, std::string fname)
{
    // Copies data to MATLAB format matrix
    mxArray * mat;
    mat = mxCreateDoubleMatrix(rows, cols, mxREAL);
    memcpy((void*)mxGetPr(mat), data, rows * cols * sizeof(double));

    // Creates output file
    MATFile * output;
    std::string matFilename = fname + ".mat"; //  Output filename
    std::string varName = "tmp"; // Storage variable in MAT file
    output = matOpen(matFilename.c_str(), "w"); // Opens MAT file for writing
    if (output == NULL) {
        printf("Error creating file");
    }

    // Adds data variable to MAT file
    int status = matPutVariable(output, varName.c_str(), mat);
    if (status != 0)
    {
        printf("Error writing mat file");
    }

    mxDestroyArray(mat); // Free up memory
}

Any help would be appreciated. Thanks in advance!

Upvotes: 0

Views: 266

Answers (1)

Paul R
Paul R

Reputation: 213170

It appears that you are running out of file handles, because you keep calling matOpen but then don't subsequently call matClose. Most systems impose an upper limit on the number of concurrently open files - it would appear that on your system this limit is 512 - there are already a few files open, so when you get to around the 508th iteration you run out of file handles.

Having said that, you should not see a crash - you have error checking on matOpen and this should fail gracefully when you try to open too many files, but evidently it doesn't!

Upvotes: 1

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