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problem compiling singleton template class


So I'm trying to implement a singleton template class, but I'm getting a
confusing 'undefined reference' when it tries to link. Here's the code
and g++'s output. Any help?

// singleton.h

template <class T>
class Singleton : public T {
public:
static T * Instance();

protected:
Singleton();
~Singleton();

private:
static Singleton<T> * instance;
};

// singleton.cpp

#include <iostream>
#include "singleton. h"

template <class T> Singleton<T> * Singleton<T>::i nstance = 0;

template <class T> T * Singleton<T>::I nstance() {
return (instance?insta nce:(instance = new Singleton<T>));
}

template <class T> Singleton<T>::S ingleton() {
std::cout << "constructi ng singleton" << std::endl;
}

template <class T> Singleton<T>::~ Singleton() {
std::cout << "destructin g singleton" << std::endl;
}

// a.h

class A {
protected:
A();
virtual ~A();
};

// a.cpp

#include "a.h"
#include <iostream>

A::A() {
std::cout << "constructi ng A" << std::endl;
}

A::~A() {
std::cout << "destructin g A" << std::endl;
}

// main.cpp

#include "a.h"
#include "singleton. h"
#include <iostream>

int main(int argc, char ** argv) {
A * a = Singleton<A>::I nstance();
return 0;
}

g++ -g -Wall -MD a.o main.o singleton.o -o a.out
main.o(.text+0x 1f): In function `main':
main.cpp:8: undefined reference to `Singleton<A>:: Instance()'
collect2: ld returned 1 exit status
make: *** [singleton] Error 1
Jul 22 '05 #1
1 2455

"Jim Strathmeyer" <st*********@nc .invalid> wrote in message
news:MY******** ***********@twi ster.southeast. rr.com...

So I'm trying to implement a singleton template class, but I'm getting a
confusing 'undefined reference' when it tries to link. Here's the code
and g++'s output. Any help?


Congratulations on asking the most frequently asked question on this group.

See the FAQ
http://www.parashift.com/c++-faq-lit...templates.html question
34.12 onwards.

john
Jul 22 '05 #2

This thread has been closed and replies have been disabled. Please start a new discussion.

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