Issue implementing basic templates

Question

Having read many links about setting up templates on classes I have got to this perplexing compiler error:

Linking...
main.obj : error LNK2019: unresolved external symbol "public: __thiscall test<int,int>::test<int,int>(int)" (??0?$test@HH@@QAE@H@Z) referenced in function _main
fatal error LNK1120: 1 unresolved externals

The offending code, as simply as possible is:

test.h

template<typename U, typename V>
class test {
public:
    test(int number);
};

test.cpp

#include "test.h"

template<typename T, typename U>
test<T, U>::test(int number){}

main.cpp

#include "test.h"

void main() {
    test<int, int> a = test<int, int>(4);
}

Clearly the previous code does nothing useful, I am simply building a model of templates to start a project. Can anyone explain what I'm not understanding about structuring this solution to meet the ends of having a templated class that can construct itself correctly?

This should be a duplication - put the template definition in the header — , Oct 15 '13 at 16:45

score 0 · Answer 1 · answered Oct 15 '13 at 16:44

0

move the implementation to the header.

answered Oct 15 '13 at 16:44

RonenKr

213
1
7

score 0 · Answer 2 · answered Oct 15 '13 at 16:46

0

Because of the way templates work, your implementation must be in the header file, not in a separate .cpp file. So your need this:

template<typename U, typename V>
class test {
public:
    test(int number)
    {
    }
};

answered Oct 15 '13 at 16:46

Gerald

23,011
10
73
102

score 0 · Answer 3 · edited May 23 '17 at 12:10

0

Besides moving implementation to the header you can also use trick shown in the question at the link template definition and declaration in separate files

edited May 23 '17 at 12:10

Community

1
1

answered Oct 15 '13 at 16:53

Igor Popov

2,588
17
20

Issue implementing basic templates

3 Answers3