模板参数中参数1处的C ++类型/值不匹配 [英] C++ type/value mismatch at argument 1 in template parameter

问题描述

好的，所以我在下面有这段代码，当我执行它时，出现以下错误:

Ok so I have this code below and when I execute it I get the following error:

type/value mismatch at argument 1 in template parameter list for ‘template<class _Tp, class _Alloc> class std::vector’
     vector<s> v;

template <class T>
class A {
public:
    struct s{T x;};
};

template <class T>
class B: public A<T> {
public:
    using A<T>::s;
    vector<s> v;
};

有人可以解释这个问题吗?

Can someone please explain the problem.

推荐答案

问题是编译器不知道 s 是类型还是值.在这种情况下，您添加 typename 或 template ，但是在我测试时，这两种方法都不起作用.直接在 vector 可以使用完整类型:

The issue is that the compiler doesn't know whether s is a type or a value. This is the case where you add typename or template, but neither of those worked when I tested. Using the full type directly in the vector does work however:

template <class T>
class B: public A<T> {
public:
    using A<T>::s;
    std::vector<typename A<T>::s> v;
};

(编辑)继续使用它是因为为什么不这样做，当然在我没有尝试过的地方需要 typename : using 行.以下代码也可以.

(Edit) Kept playing with it because why not, and of course typename was needed in the one place I didn't trying it: the using line. The following code also works.

template <class T>
class B: public A<T> {
public:
    using typename A<T>::s;
    std::vector<s> v;
};

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