你如何设置 cout 语言环境来插入逗号作为千位分隔符? [英] How do you set the cout locale to insert commas as thousands separators?

问题描述

给定以下代码:

cout << 1000;

我想要以下输出:

1,000

这可以使用 std::locale 和 cout.imbue() 函数来完成，但我担心我可能会在这里遗漏一步.你能发现吗?我目前正在复制当前语言环境，并添加千位分隔符方面，但逗号从未出现在我的输出中.

This can be done using std::locale, and the cout.imbue() function, but I fear I may be missing a step here. Can you spot it? I'm currently copying the current locale, and adding a thousands separator facet, but the comma never appears in my output.

template<typename T> class ThousandsSeparator : public numpunct<T> {
public:
    ThousandsSeparator(T Separator) : m_Separator(Separator) {}

protected:
    T do_thousands_sep() const  {
        return m_Separator;
    }

private:
    T m_Separator;
}

main() {
    cout.imbue(locale(cout.getloc(), new ThousandsSeparator<char>(',')));
    cout << 1000;
}

推荐答案

do_thousands_sep的默认实现已经返回','.看起来您应该改写 do_grouping .do_grouping 默认返回一个空字符串，表示没有分组.这意味着每组三位数字:

The default implementation of do_thousands_sep already returns ','. It looks like you should override do_grouping instead. do_grouping returns an empty string by default, which means no grouping. This means groups of three digits each:

string do_grouping() const
{
    return "3";
}

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