How to call a template Method [duplicate] - c++

Question

This question already has answers here:
Why can templates only be implemented in the header file?
(17 answers)
Closed 8 years ago.
I read that its possible to create template method. I have something like this in my code
File : Student.h
class Student
{
public:
template<class typeB>
void PrintGrades();
};
File: Student.cpp
#include "Student.h"
#include <iostream>
template<class typeB>
void Student::PrintGrades()
{
typeB s= "This is string";
std::cout << s;
}
Now in main.cpp
Student st;
st.PrintGrades<std::string>();
Now I get a linker Error:
Error 1 error LNK2019: unresolved external symbol "public: void __thiscall Student::PrintGrades<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >(void)" (??$PrintGrades#V?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std###Student##QAEXXZ) referenced in function _main
Any suggestion on what I might be doing wrong ?

Answer 1

The template is not instantiated anywhere, causing a linker error.
For templates defined in the header, the compiler will generate the instantiation by itself, because it has access to its definition. However, for templates defined in the .cpp file, you need to instantiate them yourself.
Try adding this line to the end of your .cpp file:
template void Student::printGrades<std::string>();