How can I place a matrix of unsigned characters into a field in a MATLAB structure?
How can I place a matrix of unsigned characters into a field in a MATLAB structure? I am having difficulty in using a MEX-file to receive a 20-by-2 matrix of unsigned character values in C++ and transfer them to the same size matrix that is part of a structure in MATLAB.
Prashant Kumar answered .
2025-11-20
To receive a matrix of unsigned characters into a field in a MATLAB structure, you can use our C API routines. These routines will copy the unsigned character matrix into the field of the MATLAB structure. The logical structure of an MATLAB structure is illustrated below:
mxArray *(structure) #created using mxCreateStructureMatrix
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-- mxArray *(field1) #created using mxCreate#####
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-- mxArray *(field2) #created using mxCreate#####
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-- mxArray *(field3) #created using mxCreate#####
An unsigned char is equivalent to an unsigned 8-bit integer, which you can create in your MEX-file using the mxCreateNumericArray routine:
field3 = mxCreateNumericMatrix(20, 2, mxUINT8_CLASS, mxREAL); //The above says to create a real (as opposed to complex) 20 x 2 matrix of type "uint8".
You can now add this to the structure that was previously created with the mxCreateStructMatrix using the mxSetField routine.
mxArray *structure;
mxArray *field3;
unsigned char *pdata;
structure = mxCreateStructMatrix(1, 1, 3, {"field1", "field2","field3"});
mxSetField(structure, 0, "field1", mxCreateDoubleScalar(20));
mxSetField(structure, 0, "field2", mxCreateDoubleScalar(2));
field3 = mxCreateNumericMatrix(20, 2, mxUINT8_CLASS, mxREAL);
//returns the pointer to the data part of the MATLAB array
pdata = mxGetData(field3);
// Now copy actual data into the data part of field3
for (int j = 0 ; j < 2 ; j++) {
for (int i = 0 ; i < 20 ; i++) {
pdata[20*j + i] = CppMatrix[i][j];
}
}
mxSetField(structure, 0,"field3", field3);