是 std::pair<int, std::string>订购明确?
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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