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#include <vector>
#include <iostream>
 
class data {
private:
    std::vector<char> cdata;        //   
    std::vector<double> ddata;      // container for 64-bit floating point
    char dtype;
public:
    data(char type) : cdata(10, 'c'), 
                      ddata(10, 3.00),
                      dtype(type){}
 
    template <typename T>
    void get_data(std::vector<T>& outdata) const {
        switch (dtype) {
        case 'c':
            outdata = cdata;
            break;
        case 'd':
            outdata = ddata;
            break;
        default:
            std::cerr << "Unknown data format" << std::endl;
            break;
        }
    }
 
};
 
int main ()
{
    data mydata('c');
    std::vector<double> v;
    mydata.get_data(v);
}
 

prog.cpp: In instantiation of 'void data::get_data(std::vector<T>&) const [with T = double]':
prog.cpp:35:22:   required from here
prog.cpp:18:21: error: no match for 'operator=' (operand types are 'std::vector<double>' and 'const std::vector<char>')
             outdata = cdata;
                     ^
In file included from /usr/include/c++/5/vector:69:0,
                 from prog.cpp:1:
/usr/include/c++/5/bits/vector.tcc:167:5: note: candidate: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(const std::vector<_Tp, _Alloc>&) [with _Tp = double; _Alloc = std::allocator<double>]
     vector<_Tp, _Alloc>::
     ^
/usr/include/c++/5/bits/vector.tcc:167:5: note:   no known conversion for argument 1 from 'const std::vector<char>' to 'const std::vector<double>&'
In file included from /usr/include/c++/5/vector:64:0,
                 from prog.cpp:1:
/usr/include/c++/5/bits/stl_vector.h:448:7: note: candidate: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(std::vector<_Tp, _Alloc>&&) [with _Tp = double; _Alloc = std::allocator<double>]
       operator=(vector&& __x) noexcept(_Alloc_traits::_S_nothrow_move())
       ^
/usr/include/c++/5/bits/stl_vector.h:448:7: note:   no known conversion for argument 1 from 'const std::vector<char>' to 'std::vector<double>&&'
/usr/include/c++/5/bits/stl_vector.h:470:7: note: candidate: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(std::initializer_list<_Tp>) [with _Tp = double; _Alloc = std::allocator<double>]
       operator=(initializer_list<value_type> __l)
       ^
/usr/include/c++/5/bits/stl_vector.h:470:7: note:   no known conversion for argument 1 from 'const std::vector<char>' to 'std::initializer_list<double>'

Standard output is empty