c++ - How to call a template Method -

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• why can templates implemented in header file? 13 answers

i read possible create template method. have in 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 string";     std::cout << s; } 

now in main.cpp

student st; st.printgrades<std::string>(); 

now 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 might doing wrong ?

the template not instantiated anywhere, causing linker error.

for templates defined in header, compiler generate instantiation itself, because has access definition. however, templates defined in .cpp file, need instantiate them yourself.

try adding line end of .cpp file:

template void student::printgrades<std::string>();