C++ vector to MxArray as output for a MEX function

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Nicolas Jaccard 2011-11-4

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https://ww2.mathworks.cn/matlabcentral/answers/20387-c-vector-to-mxarray-as-output-for-a-mex-function

Hi all,

I've been stuck on this for a few days; I have a function with many nested for-loops and I decided to create a MEX version in order to speed up its execution. So far so good, the compiled approach is, as expected, much faster.

I generate a non determinate number of data points that I store in an array. For now, I am creating a very large array hoping it will be big enough to store my data. But I would like it to be a tad more elegant and use dynamic arrays. Because I am adding one element at a time, I figured that re-allocating every iteration is not the most optimal approach. I then tried to use vectors (as in C++ vectors) but I ran into another issue:

I have the following:

vector<int> myVector(0);

To which I add elements using:

myVector.push_back(dataPoint);

My question is: how can I possibly copy the content of the vector at the end of my routine to an mxArray that I can thenuse as the output of my MEX function? I tried memcopy but somehow I keep getting seg faults.

Any help?

Thanks!

Nicolas

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James Tursa 2011-11-4

Please show the code you are using to do the copying.

Kaustubha Govind 2011-11-4

Also, please show us how you are constructing the mxArray.

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Answer 1

Nicolas Jaccard 2011-11-4

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https://ww2.mathworks.cn/matlabcentral/answers/20387-c-vector-to-mxarray-as-output-for-a-mex-function#answer_26923

I guess this is a typical case of actually writing the question making me realize what was wrong!

I constructed my mxArray using mxCreateNumericMatrix but I used the wrong data type, in order to be compatible with my int vector, I had to use mxUINT16_CLASS as the type flag.

Nicolas