I assume that the mask you applied in C++ was
0 -1 0
-1 4 -1
0 -1 0
and not what you gave in your comment to Oleg's reply.
If that's the case, then all you'd need to do in Matlab is to call the conv2 function, something like this:
mask = [0 -1 0; -1 4 -1; 0 -1 0];
result = conv2(image, mask);
You may need to select the right option for what to do at the boundaries of the image, to match what you did in C++.
