問題描述

我目前有一個 std::map 將一個整數(shù)值存儲到一個唯一的字符串標(biāo)識符中，我確實(shí)使用該字符串進(jìn)行查找.它主要做我想要的，除了它不跟蹤插入順序.因此，當(dāng)我迭代地圖以打印出值時，它們會根據(jù)字符串進(jìn)行排序；但我希望它們按照(第一次)插入的順序進(jìn)行排序.

I currently have a std::map<std::string,int> that stores an integer value to a unique string identifier, and I do look up with the string. It does mostly what I want, except that it does not keep track of the insertion order. So when I iterate the map to print out the values, they are sorted according to the string; but I want them to be sorted according to the order of (first) insertion.

我想過使用 vector> 代替，但我需要查找字符串并將整數(shù)值增加大約 10,000,000 次，所以我不知道std::vector 是否會明顯變慢.

I thought about using a vector<pair<string,int>> instead, but I need to look up the string and increment the integer values about 10,000,000 times, so I don't know whether a std::vector will be significantly slower.

有沒有一種方法可以使用 std::map 或者是否有另一個更適合我需要的 std 容器?

Is there a way to use std::map or is there another std container that better suits my need?

我使用的是 GCC 3.4，我的 std::map 中的值可能不超過 50 對.

I'm on GCC 3.4, and I have probably no more than 50 pairs of values in my std::map.

推薦答案

如果 std::map 中只有 50 個值，您可以將它們復(fù)制到 std::vector> 在使用適當(dāng)?shù)暮油ㄟ^ std::sort 打印和排序之前.

If you have only 50 values in std::map you could copy them to std::vector before printing out and sort via std::sort using appropriate functor.

或者你可以使用 boost::multi_index.它允許使用多個索引.在您的情況下，它可能如下所示:

Or you could use boost::multi_index. It allows to use several indexes. In your case it could look like the following:

struct value_t {
      string s;
      int    i;
};

struct string_tag {};

typedef multi_index_container<
    value_t,
    indexed_by<
        random_access<>, // this index represents insertion order
        hashed_unique< tag<string_tag>, member<value_t, string, &value_t::s> >
    >
> values_t;

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