是 std::pair<int, std::string>订购明确? [英] Is std::pair&lt;int, std::string&gt; ordering well-defined?

问题描述

似乎可以对std::vector>进行排序，它会根据int值进行排序.这是一个明确定义的事情吗?

It seems that I can sort a std::vector<std::pair<int, std::string>>, and it will sort based on the int value. Is this a well defined thing to do?

std::pair 是否有基于其元素的默认排序?

Does std::pair have a default ordering based on its elements?

推荐答案

std::pair 使用字典比较:它会根据第一个元素进行比较.如果第一个元素的值相等，则根据第二个元素进行比较.

std::pair uses lexicographic comparison: It will compare based on the first element. If the values of the first elements are equal, it will then compare based on the second element.

C++03 标准(第 20.2.2 节)中的定义是:

The definition in the C++03 standard (section 20.2.2) is:

template <class T1, class T2>
bool operator<(const pair<T1, T2>& x, const pair<T1, T2>& y);

Returns: x.first < y.first || (!(y.first < x.first) && x.second < y.second).

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