template-id does not match any template delcaration

Question

I'm getting a frustrating compiler error I can't seem to work around. It's to do with the template specialization but I can't see what's wrong...

../../include/thread/lock_guard.inl:23: error: template-id 'lock_guard<>' for 'thread::lock_guard<thread::null_mutex>::lock_guard(thread::null_mutex&)' does not match any template declaration
../../include/thread/lock_guard.inl:23: error: invalid function declaration
../../include/thread/lock_guard.inl:29: error: template-id 'lock_guard<>' for 'thread::lock_guard<thread::null_mutex>::~lock_guard()' does not match any template declaration
../../include/thread/lock_guard.inl:29: error: invalid function declaration

The code is as follows:

 #include "thread/mutex.hpp"

namespace thread {

    template <typename T>
    class lock_guard
    {
        public:
            lock_guard(T& lock);
            ~lock_guard();

        private:
            mutable T&  m_lock;
            mutable int m_state;
    };

    template <>
    class lock_guard<null_mutex>
    {
       public:
            lock_guard(null_mutex&);
            ~lock_guard();
    };

} //namespace

#include "thread/lock_guard.inl"

------------------------------------    

#include "thread/lock_guard.hpp"

namespace thread {

    template <typename T>
    lock_guard<T>::lock_guard(T& lock)
        : m_lock(lock),
          m_state(lock.lock())
    {
        /* do nothing */
    }

    template <typename T>
    lock_guard<T>::~lock_guard()
    {
        if(0 == m_state) 
        {
            m_lock.unlock();
        }
    }

    template <>
    lock_guard<null_mutex>::lock_guard(null_mutex&)
    {
        /* do nothing */
    }

    template <>
    lock_guard<null_mutex>::~lock_guard()
    {
        /* do nothing */
    }

} //namespace

Answer 1

A full class template specialization is not a template any more, it is a regular class. Hence you don't need template<> when defining its members:

lock_guard<null_mutex>::lock_guard(null_mutex&)
{
    /* do nothing */
}

lock_guard<null_mutex>::~lock_guard()
{
    /* do nothing */
}

Answer 2

也许这不是错误的原因，但是您不需要头文件中的专业化代码。