MATLAB: How to build nested mxStructs in C for use with MATLAB MEX-files or the MATLAB Compiler

Question

I would like to build a multilevel nested structure in C, either as an output from a MEX-file or as an input to a MATLAB Compiler-generated shared library.

Answer 1

Nested structures can be most easily built in C using the mxCreateStructMatrix() / mxCreateStructArray() and mxSetField() / mxSetFieldByNumber() functions.

The example file SUBSTRUCTEX.C below demonstrates the procedure in a MEX-file; the process will be similar for MATLAB Compiler-generated shared libraries. substructex.c is a modified version of the mxcreatestructarray.c example mentioned on the mxCreateStructArray documentation in the External Interfaces manual; you should first be comfortable with the workflow demonstrated in that simpler case, which you can view by executing the following MATLAB command:

doc mxCreateStructArray

Download the C-code attached below and compile it using the MEX command:

mex -v substructex.c

You can demonstrate this nested structure example by executing it, and examining the results:

a = substructex
a = 
1x4 struct array with fields:
      name
      phone
      hometown
a(2)
ans = 
          name: 'Mary Smith'
         phone: 3912
      hometown: [1x1 struct]
a(2).hometown
ans = 
         city: 'London'
      country: 'UK'