c++ - 编译器会排除未使用的模板代码吗？

Question

当您使用包含许多方法(如 vector)的模板并编译您的代码时，编译器会丢弃未使用的方法中的代码吗？

Answer 1

模板除非被使用，否则不会被实例化，所以实际上没有代码可以丢弃。

标准说 (14.7.1/10)

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. The use of a template specialization in a default argument shall not cause the template to be implicitly instantiated except that a class template may be instantiated where its complete type is needed to determine the correctness of the default argument. The use of a default argument in a function call causes specializations in the default argument to be implicitly instantiated.

因此，如果您可以避免使模板的成员函数成为虚函数，编译器将不会为它们生成任何代码(如果编译器足够聪明，这也可能适用于虚函数)。