跟踪插入顺序的 std::map ?

2021-12-10 00:00:00 dictionary c++ std insertion-order

我目前有一个 std::map 将一个整数值存储到一个唯一的字符串标识符中，我确实使用该字符串进行查找.它主要做我想要的，除了它不跟踪插入顺序.因此，当我迭代地图以打印出值时，它们会根据字符串进行排序；但我希望它们按照(第一次)插入的顺序进行排序.

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.

我想过使用 vector> 代替，但我需要查找字符串并将整数值增加大约 10,000,000 次，所以我不知道std::vector 是否会明显变慢.

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.

有没有一种方法可以使用 std::map 或者是否有另一个更适合我需要的 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 中的值可能不超过 50 对.

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

推荐答案

如果 std::map 中只有 50 个值，您可以将它们复制到 std::vector> 在使用适当的函子通过 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.它允许使用多个索引.在您的情况下，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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