有什么方法可以根据类模板类型来初始化此变量? [英] Any way to initialize this variable based on class template type?

问题描述

我有一个带有模板的 stats 类，因此它可以很灵活.不过，我是模板的新手，我认为模板的目的是使模板在用户周围变得灵活.因此，当我碰到一堵小墙时，我感觉好像做错了事.

I have a class stats with a template so that it can be flexible. I'm new to templates though, and I thought the point of them was to make it flexible around the user. So I feel like I'm doing something wrong seeing as I've hit a small wall.

#include <iostream>
#include <cstdio>
#include <iomanip>

template <typename T>
class stats
{
    private:
        int n;
        T sum;
    public:
        stats()
        {
            this->n = 0;
            this->sum = T();
        }
        void push(T a);
        void print();
};

int main()
{
    std::string tmp; // change type based on class type T
    stats<std::string> s;
    while (std::cin >> tmp) // while input is active...
    {
        s.push(tmp);
    }

    // Output & Formatting
    s.print();
    return 0;
}
template <typename T>
void stats<T>::push(T a)
{
    this->sum += a;
    ++this->n;
}
template <typename T>
void stats<T>::print()
{
    std::cout   << std::left << std::setw(4) << "N"   << "= " << n   << '\n'
                << std::left << std::setw(4) << "sum" << "= " << sum << '\n';
}

从 int main()中，理想情况下，我希望每次我想尝试其他类型时都不必自己更改tmp.在C ++中有可能吗?

From int main(), ideally, I'd like tmp to not have to be changed by myself every time I wan to try a different type. Is that possible in C++?

推荐答案

惯用的方法是公开类型别名:

The idiomatic way would be to expose a type alias:

template <typename T>
class stats
{
public:
    using value_type = T;

    // ...
};

然后在您的主目录中:

int main()
{
    stats<std::string> s;
    decltype(s)::value_type tmp;
    while (std::cin >> tmp)
    {
        s.push(tmp);
    }

    // ...
}

那样， tmp 将始终采用 T 的类型.

That way, tmp will always take the type of T.

要简化主要功能，也可以在其中使用别名:

To even simplify your main function, you can use an alias there too:

int main()
{
    using stats_t = stats<std::string>;
    stats_t s;
    stats_t::value_type tmp;
    while (std::cin >> tmp)
    {
        s.push(tmp);
    }

    // ...
}

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