class template cpp, hpp, cpp

Question

I have this class in my .hpp file

template<class T = int>
class Matrix
{
    public:
    Matrix();
}

and I have this Matrix.cpp file

#include "Matrix.hpp"
template<class T>
Matrix<T>::Matrix()
{
    vector<T> vecN(1, 0);
    _matrix.resize(1, vecN);
    _rows = 1;
    _cols = 1;
}

but it won't work, when adding a main

#include "Matrix.hpp"

int main(int argc, char** argv)
{
    Matrix<int> test();
    return 0;
}

i get a very weird error saying

main.cpp:19: undefined reference to Matrix<int>::Matrix(unsigned int, unsigned int)' main.cpp:19:(.text+0x2d): relocation truncated to fit: R_X86_64_PC32 against undefined symbol Matrix<int>::Matrix(unsigned int, unsigned int)

Dominique McDonnell · Accepted Answer · 2015-09-03T03:33:57.387

3

Template code must be in the header, unless it is for specialisations.

This is because the template is used to generate the actual class when you use it.

edited Sep 03 '15 at 03:33

answered Sep 03 '15 at 03:33

Dominique McDonnell

2,510
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25

what does specialisations mean? – Mumfordwiz Sep 03 '15 at 03:33
@Mumfordwiz If you have a template class `A`, you can additionally write a separate eg. `A` with different code, then for float the second class will be used, and for everything else the first. – deviantfan Sep 03 '15 at 03:35
@deviantfan got it. Thanks! – Mumfordwiz Sep 03 '15 at 03:37

class template cpp, hpp, cpp

1 Answers1