模板参数中“T”和“const T”之间有什么区别吗？

Is there any difference between following 2 syntax:

以下2种语法之间有什么区别：

template<int N> struct A;         // (1)

and

和

template<const int N> struct A;   // (2)

Any general guideline for when to use each syntax ?

何时使用每种语法的一般准则？

3 个解决方案

#1

No.

没有。

§14.1 [temp.param] p5

§14.1[temp.param] p5

[...] The top-level cv-qualifiers on the template-parameter are ignored when determining its type.

[...]模板参数的*cv限定符在确定其类型时会被忽略。

#2

I found this doing a quick search of the standard:

我发现这样可以快速搜索标准：

template<const short cs> class B { };
template<short s> void g(B<s>);
void k2() {
    B<1> b;
    g(b); // OK: cv-qualiﬁers are ignored on template parameter types
}

The comment says they are ignored.

评论说他们被忽略了。

I'll recommend not using const in template parameters as it's unnecessary. Note that it's not 'implied' either - they're constant expressions which is different from const.

我建议不要在模板参数中使用const，因为它是不必要的。请注意，它也不是“暗示” - 它们是与const不同的常量表达式。

#3

The choice of int was probably a bad idea, it makes a difference for pointers though:

int的选择可能是一个坏主意，但它对指针有所不同：

class A
{
public:
    int Counter;
};

A a;


template <A* a>
struct Coin
{
    static void DoStuff()
    {
        ++a->Counter; // won't compile if using const A* !!
    }
};

Coin<&a>::DoStuff();
cout << a.Counter << endl;

#1

No.

没有。