在STL地图中，最好使用map :: insert than []吗？ [英] In STL maps, is it better to use map::insert than []?

问题描述

前一段时间，我和一位同事讨论了如何在STL 中插入值地图。我喜欢
map [key] = value;
因为它感觉很自然，很清楚，而他更喜欢
map.insert（std :: make_pair（key，value））

A while ago, I had a discussion with a colleague about how to insert values in STL maps. I preferred map[key] = value; because it feels natural and is clear to read whereas he preferred map.insert(std::make_pair(key, value))

我刚刚问他，我们都不记得原因为什么插入更好，但我相信这不仅仅是一种风格偏好，而是有一个技术原因，如效率。 SGI STL参考资料简单地说：严格来说，这个成员函数是不必要的存在只是为了方便。

I just asked him and neither of us can remember the reason why insert is better, but I am sure it was not just a style preference rather there was a technical reason such as efficiency. The SGI STL reference simply says "Strictly speaking, this member function is unnecessary: it exists only for convenience."

有人可以告诉我这个原因，还是我只是梦想有一个？

Can anybody tell me that reason, or am I just dreaming that there is one?

推荐答案

当你写

map[key] = value;

没有办法告诉您是否替换 c c $ c c>与值。

there's no way to tell if you replaced the value for key, or if you created a new key with value.

map :: insert（） 只会创建：

map::insert() will only create:

using std::cout; using std::endl;
typedef std::map<int, std::string> MyMap;
MyMap map;
// ...
std::pair<MyMap::iterator, bool> res = map.insert(std::make_pair(key,value));
if ( ! res.second ) {
    cout << "key " <<  key << " already exists "
         << " with value " << (res.first)->second << endl;
} else {
    cout << "created key " << key << " with value " << value << endl;
}

对于我的大多数应用程序，我通常不在乎我是否创建或替换，所以我使用更容易阅读 map [key] = value 。

For most of my apps, I usually don't care if I'm creating or replacing, so I use the easier to read map[key] = value.

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