Date: Feb 14, 2014 6:01 AM
Author: Aaronne
Subject: How to output a 2D integer array using Matlab mex?

Hi smart guys,

I got a follow up question about Matlab mex function input/output 2D array format. For example, I have a variable '`outputBuff`' defined as C++ 2D integer array. After processing it, I want to output it as a 'plhs' (parameter at left hand side). Not sure how to do this.

int** outputBuff;

size_t col_outputBuff = mxGetN(prhs[4]);
size_t row_outputBuff = mxGetM(prhs[4]);

// Allocate the memory for 2D array
outputBuff = (int **)mxCalloc(col_outputBuff, sizeof(int*));

for(int x = 0; x < col_outputBuff; x++) {
outputBuff[x] = (int *) mxCalloc(row_outputBuff, sizeof(int));

// Read in the data
for (int col=0; col < col_outputBuff; col++) {
for (int row=0; row < row_outputBuff; row++) {
outputBuff[col][row] = ((int *)mxGetPr(prhs[4]))[row+col*row_outputBuff];

Then output it as `plhs`

const mwSize dims[] = {col_outputBuff, row_outputBuff};
plhs[0] = mxCreateNumericArray(2, dims, mxINT32_CLASS, mxREAL);

mxArray *outputMatrix;
outputMatrix = mxCreateNumericMatrix(col_outputBuff, row_outputBuff, mxINT32_CLASS, mxREAL);
outputBuff[0] = (int *)mxGetPr(outputMatrix);
outputMatrix = (mxArray *)mxGetData(plhs[0]);

The codes can be compiled but output all zeros not as expected. Could you give me some hints? Thanks a lot. A.