模板类的虚成员函数什么时候实例化? [英] When the virtual member functions of a template class instantiated?

问题描述

我知道模板类的普通成员函数在第一次使用时都会被实例化.但是这不能用于虚拟成员函数，因为它可以通过基类指针访问.这是否意味着一旦模板类被实例化，虚成员函数就会被实例化?如果没有，什么时候?

I know that the normal member function of a template class will be instantiated whenever it is used for the first time. But this cannot be done for the virtual member function as it can be accessed through a base class pointer. Does this mean that virtual member functions will be instantiated as soon as the template class is instantiated? If not, when?

推荐答案

14.7.1/9 in C++03:

实现不应隐式实例化不需要实例化的函数模板、成员模板、非虚拟成员函数、成员类或类模板的静态数据成员.如果虚拟成员函数不会被实例化，则实现是否隐式实例化类模板的虚拟成员函数是未指定的.

An implementation shall not implicitly instantiate a function template, a member template, a non-virtual member function, a member class or a static data member of a class template that does not require instantiation. It is unspecified whether or not an implementation implicitly instantiates a virtual member function of a class template if the virtual member function would not otherwise be instantiated.

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