Evaluate MATLAB Statements from C++

Evaluation of MATLAB Statements

These examples show you how to evaluate MATLAB^® statements from C++ using the MATLABEngine::eval and MATLABEngine::evalAsync member functions. These member functions are similar to the MATLAB eval function. The MATLABEngine::eval and MATLABEngine::evalAsync functions do not return the results of evaluating the MATLAB statement.

Use MATLABEngine::eval and MATLABEngine::evalAsync when you do not need to pass arguments from C++ or return values to C++. The statements that you execute with these functions can access variables in the MATLAB workspace.

Here are some things to know about evaluating statements in MATLAB.

These functions pass statements to MATLAB in as a matlab::engine::String.
Convert an std::string to a matlab::engine::String using the u"…" literal or the utility function matlab::engine::convertUTF8StringToUTF16String.
The input arguments named in the string must exist in the MATLAB workspace.
You can assign the results of the evaluation to variables within the statement string. The variable that you assign in the statement is created in the MATLAB base workspace.
MATLAB does not require you to initialize the variables created in the statement.
You can store the standard output from MATLAB functions and error messages in stream buffers.

Evaluate Mathematical Function in MATLAB

This example uses MATLABEngine::eval to evaluate a series of MATLAB statements. These statements:

Evaluate a mathematical function over a specified domain using meshgrid and exp.
Create a graph of the function using surf.
Export the graph to a JPEG file using print.

Here is the equivalent MATLAB code.

[X, Y] = meshgrid(-2:0.2:2);
Z = X .* exp(-X.^2 - Y.^2);
surf(Z)
print('SurfaceGraph', '-djpeg')
currentFolder = pwd;

Here is the C++ code to execute these statements in MATLAB.

#include "MatlabDataArray.hpp"
#include "MatlabEngine.hpp"
#include <iostream>

void evalSurfaceGraph() {
    // Evaluate functions in MATLAB

    using namespace matlab::engine;

    // Start MATLAB engine synchronously
    std::unique_ptr<MATLABEngine> matlabPtr = startMATLAB();

    // Evaluate commands in MATLAB
    matlabPtr->eval(u"[X, Y] = meshgrid(-2:0.2:2);");
    matlabPtr->eval(u"Z = X .* exp(-X.^2 - Y.^2);");
    matlabPtr->eval(u"surf(Z)");
    matlabPtr->eval(u"print('SurfaceGraph', '-djpeg')");
    matlabPtr->eval(u"currentFolder = pwd;");

    // Get the name of the folder containing the jpeg file
    matlab::data::CharArray currentFolder = matlabPtr->getVariable(u"currentFolder");
    std::cout << "SurfaceGraph.jpg written to this folder: " << 
          currentFolder.toAscii() << std::endl;
}

For information on how to setup and build C++ engine programs, see Requirements to Build C++ Engine Applications.