問題描述

前段時間和同事討論如何在STL中插入值地圖.我更喜歡 map[key] = value; 因為它感覺自然并且清晰易讀，而他更喜歡 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)).

我剛剛問過他，我們都不記得為什么 insert 更好的原因，但我確信這不僅僅是一種風格偏好，而是有一個技術原因，比如效率.SGI STL 參考 簡單地說:嚴格來說，這個成員函數是不必要:它的存在只是為了方便."

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."

誰能告訴我這個原因，還是我只是在夢想有一個?

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

推薦答案

當你寫作時

map[key] = value;

無法判斷您是否替換了key的value，或者您是否創建了一個新的key 和 value.

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

map::insert() 只會創建:

using std::cout; using std::endl;
typedef std::map<int, std::string> MyMap;
MyMap map;
// ...
std::pair<MyMap::iterator, bool> res = map.insert(MyMap::value_type(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;
}

對于我的大部分應用，我通常不在乎我是創建還是替換，所以我使用更容易閱讀的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.

這篇關于在 STL 映射中，使用 map::insert 是否比使用 [] 更好?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！