Mex function error after completion

Question

I have a C mex file that runs correctly, but MATLAB crashes with segfault after it executes. Since it crashes after the program ends, it makes me think that automatically freeing the allocated MATLAB memory is causing a problem. However, I am freeing my dynamically allocated variables and not trying to free up the mxArray structures. Please look and see if you can help me determine why this causes MATLAB to crash.

#include <mex.h> #include <matrix.h> #include <stdio.h> void mexFunction( int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) { /* Declare variables. */ int i ,j, numdims, *ipos, count; const mwSize *dim_array; mwSize size; double *pos, rad; /* Ingest inputs. */ numdims = mxGetNumberOfDimensions(prhs[0]); dim_array = mxGetDimensions(prhs[0]); rad = mxGetScalar(prhs[1]); pos = mxGetData(prhs[0]); size = dim_array[0]*dim_array[1]; ipos = (int*) mxMalloc(size); for (i = 0; i < size; i++) ipos[i] = (int) (pos[i]*rad); count = 0; for (i = 0; i < size; i+=2) for (j = i + 2; j < size; j+=2) if (ipos[i] == ipos[j]) if (ipos[i+1] == ipos[j+1]) count++; mxFree(ipos); /* Generate output */ plhs[0] = mxCreateDoubleScalar(count); printf("\nProgram finished executing!\n"); } 

Thanks in advance for your help!

Edit: I should also note that program entries should be (in order) a 2 xn matrix and a scalar, where n can be any positive integer. The actual program correctly checks the sizes, but I did not use these lines to save code space.

Answer 1

After writing a couple of hundred programs with dynamic memory allocation, I am a little ashamed to say that the error was like this:

Replace

  ipos = (int*) mxMalloc(size); 

with

  ipos = (int*) mxMalloc(size*sizeof(int)); 

It always seems like the dumbest mistakes that dodge me. I would like to thank everyone who could take a minute or two to look at the mail.

Answer 2

UPD You are right - when the matrix becomes larger, it falls :)

So, I think I have an idea:

try changing two lines of code

 plhs[0] = mxCreateDoubleMatrix(1, 1, mxREAL); mxGetPr(plhs[0])[0] = (double) count; 

for a new single line

 plhs[0] = mxCreateDoubleScalar(count); 

After I did this, it no longer crashes.