Size limit in MATLAB MEX-files

Question

I'm new to Matlab mex. I'm trying to write a mex function which in turn will take the structure data from a .cpp file and use it in Matlab.

I came to know that plhs and prhs are the pointers to an array which hold the output data and input data respectively, each element of type mxArray.

Since structure size can be large, Is there any maximum size limit for the plhs and prhs array to hold the data ? If so, What are the alternate ways?

Answer 1

As far as I've researched the size of arrays that can be handled depends on the API you compile your mex files with. You can choose the API by adding the corresponding flag in your compiling instruction. The details are in the matlab documentation under "api-release specific API".

There are 4 options avaliable: -R2017b (default) -R2018a -largeArrayDims and -compatibleArrayDims.

In term of array size -R2017b (default) -R2018a and -largeArrayDims use the Large-array-handling API which according to the matlab mex documentation can handle arrays over 2³¹-1 and, according to the API documentation should be able to handle arrays up to 2⁴⁸-1 elements and sparse arrays up to 2⁴⁸-2.

Only the last option, -compatibleArrayDims won't handle arrays above 2³¹-1

Apart from array size those options will change the way a few data types are handled, noticeably complex types and graphics object.

So in short:

• -R2017b (default) : 2⁴⁸-1 elements per array
• -R2018a : 2⁴⁸-1 elements per array
• -largeArrayDims : 2⁴⁸-1 elements per array
• -compatibleArrayDims 2³¹-1 elements per array

Finally if you want to handle larger object the solution I see would be to write your results in files (.txt or .csv for example) in the c-part of your code and read them back in the matlab part in whole or in chunks.

Hope this helped. I'm new in here so feel free to correct me if I made a mistake or disregarded the etiquette.