Using C++ Mex Function how to get std::string argument?

This seems like it should be simple, but I can't get either it to compile or not fail during runtime. Basically I need to have the Mex Function have 2 parameters which are both strings, and will be passed through to C++ functions inside. Can someome tell me how to go from matlab::mex::ArgumentList input, to 2 std::strings? I guess also what would function call look like from Matlab side?

Thanks,

Answer 1

[Karola Gurrath]

I got the same problem yesterday and this is the solution I found. Maybe this is not the best way to get a std::string but it works and I could not find anything else...

Matlab-Code:

cellArray{1} = "string1";
cellArray{2} = "string2";
myMexFunction(cellArray);

myMexFunction:

using namespace matlab::data;
using matlab::mex::ArgumentList;

class MexFunction : public matlab::mex::Function
{
    std::shared_ptr<matlab::engine::MATLABEngine> matlabPtr = getEngine();
    ArrayFactory factory;
    
    public:
    void operator()(ArgumentList outputs, ArgumentList inputs)
    {
      CellArray imageCell = std::move(inputs[0]);
      
      TypedArrayRef<MATLABString> inArrayRef1 = imageCell[0];
      std::string string1 = std::string(inArrayRef1[0]);
      
      TypedArrayRef<MATLABString> inArrayRef2 = imageCell[1];
      std::string string2 = std::string(inArrayRef2[0]);
      
      // do something with string1 und string2...
    }
}

Answer 2

[cui,xingxing]

matlab code

input1 = "string1";
input2 = "string2";
myMexFunction(input1,input2);

mex c++ code

using namespace matlab::data;
using matlab::mex::ArgumentList;

class MexFunction : public matlab::mex::Function
{
    std::shared_ptr<matlab::engine::MATLABEngine> matlabPtr = getEngine();
    ArrayFactory factory;
    
    public:
    void operator()(ArgumentList outputs, ArgumentList inputs)
    {
      std::string string1 = std::string(inputs[0][0]);
      std::string string2 = std::string(inputs[1][0]);
      
      // or use following code
      //std::string string1 = 
      //      matlab::engine::convertUTF16StringToUTF8String(inputs[0][0]);
      //std::string string2 = 
      //      matlab::engine::convertUTF16StringToUTF8String(inputs[1][0]);
      
      
      // do something with string1 und string2...
    }
}

input1/2 argument is one string scalar in matlab, but it also represent 1 by 1 string matrix, so

directly specify sub-index [0][0] in c++.

BTW, to prevent matlab crash from incorrect input, It is best to have a check-uphad

if (inputs[0].getType() != matlab::data::ArrayType::MATLAB_STRING) {
    matlabPtr->feval(u"error",
    0, std::vector<matlab::data::Array>({factory.createScalar("The first input must string scalar")}));
    }