模板类可以在 C++ 中有静态成员吗
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Can template classes have static members in C++
提问by rubixibuc
Can a template class in C++ have static members? Since it doesn't exist and is imcomplete before it is used, is this possible?
C++ 中的模板类可以有静态成员吗？由于它不存在并且在使用之前是不完整的，这可能吗？
回答by Potatoswatter
Yes. The static member is declared or defined inside the template< … > class { … }block. If it is declared but not defined, then there must be another declaration which provides the definition of the member.
是的。静态成员在template< … > class { … }块内声明或定义。如果已声明但未定义，则必须有另一个声明提供成员的定义。
template< typename T >
class has_static {
// inline method definition: provides the body of the function.
static void meh() {}
// method declaration: definition with the body must appear later
static void fuh();
// definition of a data member (i.e., declaration with initializer)
// only allowed for const integral members
static int const guh = 3;
// declaration of data member, definition must appear later,
// even if there is no initializer.
static float pud;
};
// provide definitions for items not defined in class{}
// these still go in the header file
// this function is also inline, because it is a template
template< typename T >
void has_static<T>::fuh() {}
/* The only way to templatize a (non-function) object is to make it a static
data member of a class. This declaration takes the form of a template yet
defines a global variable, which is a bit special. */
template< typename T >
float has_static<T>::pud = 1.5f; // initializer is optional
A separate static member is created for each parameterization of the template. It is not possible to have a single member shared across allclasses generated by the template. For that, you must define another object outside the template. A partially-specialized traits class might help with that.
为模板的每个参数化创建一个单独的静态成员。不可能在模板生成的所有类之间共享单个成员。为此，您必须在模板之外定义另一个对象。部分专门化的特征类可能会对此有所帮助。
