Question

I want to use iterators in template class method.
Here is my code: (testclass.h)

template<typename T, typename container>
class TestClassX
{
public:
    void gen(typename container::iterator first );
};

and file testclass.cpp:

template<typename T, typename container>
void TestClassX<T, container>::gen(typename container::iterator first)
{

}

When i try to run it:

TestClassX<unsigned, std::vector<unsigned> > testx;
testx.gen(it);

I get an error:

Error:undefined reference to `TestClassX<unsigned int, std::vector<unsigned int, std::allocator<unsigned int> > >::gen(__gnu_cxx::__normal_iterator<unsigned int*, std::vector<unsigned int, std::allocator<unsigned int> > >)'

I use mingw32 4.4

I want to have a class that can write to different containers like std::vector, std::list, QVector or QList all that have STL-style iterators.

Answer 1

Template class methods must be defined in the header file. When you use a template class, the compiler actually compiles a version of that class for the given template parameters. Therefore, it is a requirement that the body of each method is available when including the header file.

Remove you source file and include the body in testclass.h:

template<typename T, typename container>
class TestClassX
{
public:
    void gen(typename container::iterator first ) {

    }
};