特化需要在命名空间里做，不能在类中直接特化一个类模板，但可以放到类外来做。也可在类之内用偏特化，然后传入一个dummy template argument。
来源：https://stackoverflow.com/questions/3052579/explicit-specialization-in-non-namespace-scope
template<typename T>
class CConstraint
{
public:
CConstraint()
{
}
virtual ~CConstraint()
{
}
template <typename TL> void Verify(int position, int constraints[]) { } template <> void Verify<int>(int, int[]) { } }; Compiling this under g++ gives the following error: Explicit specialization in non-namespace scope 'class CConstraint' In VC, it compiles fine. Can anyone please let me know the workaround? 原因： VC++ is non-compliant in this case - explicit specializations have to be at namespace scope. C++03, §14.7.3/2: An explicit specialization shall be declared in the namespace of which the template is a member, or, for member templates, in the namespace of which the enclosing class or enclosing class template is a member. An explicit specialization of a member function, member class or static data member of a class template shall be declared in the namespace of which the class template is a member. Additionally you have the problem that you can't specialize member functions without explicitly specializing the containing class due to C++03, §14.7.3/3, so one solution would be to let Verify() forward to a, possibly specialized, free function:namespace detail { template <typename TL> void Verify (int, int[]) {} template <> void Verify<int>(int, int[]) {} } template<typename T> class CConstraint { // ... template <typename TL> void Verify(int position, int constraints[]) { detail::Verify<TL>(position, constraints); } };
来源：https://www.zhihu.com/question/54468727
class A {
public:
template <typename T, typename = void> struct B { T value; }; template <typename X> struct B<int, X> { bool value; }; B<double> dvalue; B<int> ivalue; };