When I use template function in my class TestClass. The complier will throw out a Link Error below.

TestClass.h 

template
    
         T foo(T a, T b);
    

TestClass.cpp 

   

template
    
         T TestClass::foo(T a, T b) {
  return a; }
    

Client.cpp 

TestClass testClass; testClass.foo(0, 1);

Link Error 

Error    1    error LNK2019: unresolved external symbol "public: int __cdecl TestClass::foo
    
     (int,int)" (??$foo@H@TestClass@@QAAHHH@Z) referenced in function "private: bool __cdecl Client::TestFunction()" (?TestFunction@Client@@@Z)    Client.obj
    

There are some approach we can use to fix this issue. I prefer to use the implementation header to fix that issue. 

Add a new file called TestClass_impl.h and move all the template functions from TestClass.cpp to TestClass_impl.h

Include TestClass_impl.h into TestClass.h

TestClass.h 

class TestClass {
  template
    
         T foo(T a, T b); }; #include "TestClass_impl.h"
    

All done.

    本文转自Jake Lin博客园博客，原文链接：http://www.cnblogs.com/procoder/archive/2010/06/29/How-to-Separate-the-Implementation-and-Definition-of-Template-Function-in-CPP.html，如需转载请自行联系原作者