undefined reference with a static instance

问题

I am currently porting some code from Visual Studio to Mingw GCC. It seems there is a problem when I attempt to use a static variable . This code works fine in Visual studio so I am not sure what the problem might be here. I have pasted an outline of what the code looks like. If this is insufficient I could put in more.

Header file: .h
namespace LG_Wrapper
{
    template <LG_Thread Thread>
    class EffectApplication : public ktApplication
    {
    public:
    static EffectApplication<Thread>& GetInstance();
    protected:
        .....
        .....
        static boost::recursive_mutex mResource;
      }
}

DECLARE_LEGACY_TYPES(EffectApplication);


Source File: .cpp
namespace LG_Wrapper
{

    template<>
    boost::recursive_mutex  EffectApplication<LG_Thread_NAME>::mResource;  //LG_Thread_NAME type discussed below

    template <LG_Thread Thread>
    EffectApplication<Thread>& EffectApplication<Thread>::GetInstance()
    {
        boost::recursive_mutex::scoped_lock mutex( mResource ); //Error with mResource

        static EffectApplication<Thread> instance;
        return instance;
    }
    ....
}

Now I am not sure about the LG_Thread_NAME type. After going through the code I noticed that I define the following in the project settings

LG_THREAD_NAME=GAME

This definition comes into play with this macro somewhere else in the code

#define DECLARE_LEGACY_TYPES(...)

I am having issue accessing mResource The code builds fine if I comment out the statement

boost::recursive_mutex::scoped_lock mutex( mResource );

Any suggestions on why I might be getting the following error with the above code ?

(.text$_ZN10KT_Wrapper17EffectApplicationILNS_9LT_ThreadE0EE11GetInstanceEv[_ZN10LT_Wrapper17EffectApplicationILNS_9LT_ThreadE0EE11GetInstanceEv]+0x11): undefined reference to `LT_Wrapper::EffectApplication<(LT_Wrapper::LT_Thread)0>::mResource'

Update: I am certain that there is something wrong with the variable mResource because in the static method. If I do this it builds fine

  boost::recursive_mutex l;
boost::recursive_mutex::scoped_lock mutex( l );

Duplicate Question Issue: I am not sure how this question is a duplicate of the links provided. In all the links provided the ops have not initialized their static variables. Here I have initialized my static variable outside the class.

回答1:

The initialization

template<>
boost::recursive_mutex  EffectApplication<LG_Thread_NAME>::mResource;

still is not correct, since you initialize mResource not for all template parameter, but only for specialization with LG_Thread_NAME. So I guess when you try to access it with some another template parameter you've got an error.

Correct way is like this

template<LG_Thread Thread>
boost::recursive_mutex  EffectApplication<Thread>::mResource;

Also I'm not sure with my answer because the error says that the problem is with LT_Wrapper class and template parameter (LT_Wrapper::LT_Thread)0 looks strange to me.

来源：https://stackoverflow.com/questions/29662190/undefined-reference-with-a-static-instance

标签

c++

linker-errors

static-variables