std :: inserter为std :: set使用.begin()与.end()之间有区别吗? [英] Is there a difference between using .begin() vs .end() for std::inserter for std::set?

问题描述

it1和it2之间是否有区别?

If there is any difference between it1 and it2?

std::set<sometype> s;

auto it1 = std::inserter(s, s.begin());
auto it2 = std::inserter(s, s.end());

推荐答案

在实践中并不多.如果要将大量已有的order元素插入到空的set中，第二个会更快一些，但是仅此而已. std::insert_iterator用迭代器调用insert； std::set将其解释为提示，如果插入紧接在提示之前，则以恒定时间(而不是lg n)插入. (实际上，如果set为空，我认为两者都会做完全相同的事情.)

In practice, not much. If you're inserting a large number of already in order elements into an empty set, the second will be somewhat faster, but that's about it. std::insert_iterator calls insert with the iterator; std::set interprets it as a hint, and inserts in constant time (rather than lg n) if the insertion is immediately before the hint. (Actually, if the set is empty, I think both will do exactly the same thing.)

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