Calling C function generated in MATLAB coder

I've been writing code to (attempt to) efficiently reshape large h5 datasets. I'm curious if compiling it into a C-function makes it faster so I have used MATLAB coder to do that, as my experience in C is next to 0.

The original function is of the form

camData = read_streamLEDbttrLogic(eventStream,attributes,LEDtime_ms,macroRate)

eventStream is a column vector, attributes is a structure with attributes read from file, LEDtime_m and macroRate are both scalar doubles.

When loading in the compiled library and looking at the function with libfunctions I get the below output.

[emxArray_uint32_TPtr, struct0_TPtr, struct1_TPtr] read_streamLEDbttrLogic(emxArray_uint32_TPtr, struct0_TPtr, double, double, struct1_TPtr)

I'm just not terribly sure how to call it correctly in MATLAB. When I try to this happens

[a,b,c] = calllib('read_streamLEDbttrLogic','read_streamLEDbttrLogic',eventStream,att,LEDtime_ms,macroRate);
Error using calllib
No method with matching signature.

Am I totally off the mark here and need to recompile or am I just being an idiot with the syntax? The documentation around calling C functions is pretty lax and I cant figure out where it is going wrong.

[Walter Roberson]

Note that MATLAB Coder does not generate code to operate on multiple cores, so it is common that the code generated by MATLAB Coder is overall slower than interpreted MATLAB.

A lot depends on what is being calculated. If you have non-vectorized code that is not doing matrix calculations (such as eig()) then the code generated by MATLAB Coder can certaintly be faster for that kind of code.

Answer 1

[ProblemSolver]

The issue is that MATLAB Coder has generated C code that expects input arguments of specific types like emxArray_uint32_TPtr instead of just a normal MATLAB array. This is needed for the C code to know how to interpret the MATLAB data, but makes calling it a bit more complex.

Here is one way to call the compiled C function correctly from MATLAB:

1. Convert the MATLAB arrays to the expected C types:

eventStream_c = libpointer('uint32Ptr',eventStream); % emxArray_uint32_TPtr 
att_c = libstruct('struct0_TPtr', attributes); % struct0_TPtr

1. Call the C function, passing the libpointer/libstruct objects:

[out1, out2, out3] = calllib('read_streamLEDbttrLogic', 'read_streamLEDbttrLogic', eventStream_c, att_c, LEDtime_ms, macroRate);

1. Convert outputs back to MATLAB arrays:

eventStream_out = get(out1, 'Value');
attributes_out = get(out2,'Value');

This allows passing MATLAB data in a way the C code can interpret correctly. The Coder documentation has more details on interoperating with C code.

I hope this helps.