CODEWITHSUNDEEP
c++templatesconstantsstatic-members
Duckdoom5
Duckdoom5

Reputation: 764

How to define a static const variable of a template class

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.

Upvotes: 10

Views: 9516

Answers (2)

Jarod42
Jarod42

Reputation: 218323

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

Upvotes: 13

SergeyA
SergeyA

Reputation: 62613

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);

Upvotes: 2

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