How to define a static const variable of a template class

问题

I'm trying to make a vector class with predefined static constants for up, right and forward because these should be the same in all cases. How should this be defined and is it even possible?

I'm trying to do something like this:

template <class T> class vec3
{
public:
    vec3(T x = 0, T y = 0, T z = 0) :
        x(x),
        y(y),
        z(z)
    {
    }

    static const vec3<T> right;
    static const vec3<T> up;
    static const vec3<T> forward;

    T x, y, z;
}

cpp:

#include "vec3.h"

template <typename T>
const vec3<T>::right(1, 0, 0);

template <typename T>
const vec3<T>::up(0, 1, 0);

template <typename T>
const vec3<T>::forward(0, 0, 1);

This results in a syntax error.

回答1:

It should be (all in header (you may use .inl or .hxx if you want to split declaration from definition)):

template <class T> class vec3
{
public:
    vec3(T x = 0, T y = 0, T z = 0) :
        x(x),
        y(y),
        z(z)
    {
    }

    static const vec3 right;
    static const vec3 up;
    static const vec3 forward;

    T x, y, z;
};

template <typename T> const vec3<T> vec3<T>::right(1, 0, 0);
template <typename T> const vec3<T> vec3<T>::up(0, 1, 0);
template <typename T> const vec3<T> vec3<T>::forward(0, 0, 1);

Demo

回答2:

template <class T> class vec3
{
public:
    vec3(T x = 0, T y = 0, T z = 0) :
        x(x),
        y(y),
        z(z)
    {
    }

    static const vec3 right;
    static const vec3 up;
    static const vec3 forward;

    T x, y, z;
};


template <typename T>
const vec3<T> vec3<T>::right(1, 0, 0);

template <typename T>
const vec3<T> vec3<T>::up(0, 1, 0);

template <typename T>
const vec3<T> vec3<T>::forward(0, 0, 1);

来源：https://stackoverflow.com/questions/34026555/how-to-define-a-static-const-variable-of-a-template-class

标签

c++

templates

const

static-members