C++ Interface Workaround for Class Templates With Missing Instantiations

My C++ code  includes class templates with missing or incomplete instantiation. How can I include these templates in my C++ Interface?

Answer 1

[MathWorks Support Team]

A MATLAB interface to a C++ library does not support uninstantiated template classes. To work around this limitation, use a wrapper class to create instantiations for the data types that your project uses.

This example shows how to create a wrapper header file to use a template class with missing instantiations with MATLAB's Cpp Interface.

1. 

Example code with class Pairs

2.  Create a wrapper header file

3.  Generate the library definition for the MATLAB Interface

4.  Build the library

5. Use the library

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source code

used in this example. *****

1. 

Example code with class Pairs

In this example, the class Pairs in this Templates.hpp header file is not instantiated.

// Header for Template class
#ifndef templates_Header
#define templates_Header

template <class T>
class Pairs { 
public:
    T val1;
    T val2;
    Pairs() : val1(0), val2(0) {}
    Pairs(T first, T second) : val1(first), val2(second) {}
    T getVal1() {
        return val1;
    }
    T getVal2() {
        return val2;
    }
};
#endif

2.  Create a wrapper header file

To include the Pairs class, create this wrapper header file TemplatesWrapper.hpp. Assume that Pairs supports int and double data types.

//Wrapper to instantiate template class Pairs
#include "Templates.hpp"

/* Data types that will be used for Pairs class. */
template class Pairs<int>;
template class Pairs<double>;

 3. Generate the library definition for the MATLAB Interface

In this example, TemplatesWrapper.hpp and Templates.hpp are in the same folder.

clibgen.generateLibraryDefinition(["TemplatesWrapper.hpp","Templates.hpp"],"PackageName","Templates","Verbose",true)

4. Build the library

build(defineTemplates)
addpath('Templates')

5. Use the library

Create Pairs objects and call the getVal1 and getVal2 functions.

Pairs1 = clib.Templates.Pairs_int_(2,3);
Val1 = Pairs1.getVal1;
Pairs2 = clib.Templates.Pairs_double_(4.5,10.9);
Val2 = Pairs2.getVal2;
Pairs3 = clib.Templates.Pairs_int_(4.3,10.9);
Val2 = Pairs3.getVal2;