我对矢量查找vs地图查找很好奇，并为它编写了一个小测试程序…它似乎是矢量总是更快的方式，我使用它…这里还有什么我应该考虑的吗？测试有任何偏颇吗？运行的结果是在底部…它以纳秒为单位，但gcc似乎不支持在我的平台上使用它。

使用字符串进行查找当然会改变很多事情。

我使用的编译行如下:g++-o3-std=C++0x-o lookup lookup.cpp

#include <iostream>
#include <vector>
#include <map>
#include <unordered_map>
#include <chrono>
#include <algorithm>

unsigned dummy = 0;

class A
{
public:
    A(unsigned id) : m_id(id){}

    unsigned id(){ return m_id; }
    void func()
    {
        //making sure its not optimized away
        dummy++;
    }
private:
    unsigned m_id;
};

class B
{
public:
    void func()
    {
        //making sure its not optimized away
        dummy++;
    }
};

int main()
{
    std::vector<A> v;
    std::unordered_map<unsigned, B> u;
    std::map<unsigned, B> m;

    unsigned elementCount = 1;

    struct Times
    {
        unsigned long long v;
        unsigned long long u;
        unsigned long long m;
    };
    std::map<unsigned, Times> timesMap;

    while(elementCount != 10000000)
    {
        elementCount *= 10;
        for(unsigned i = 0; i < elementCount; ++i)
        {
            v.emplace_back(A(i));
            u.insert(std::make_pair(i, B()));
            m.insert(std::make_pair(i, B()));
        }


        std::chrono::time_point<std::chrono::steady_clock> start = std::chrono::high_resolution_clock::now();
        for(unsigned i = 0; i < elementCount; ++i)
        {
            auto findItr = std::find_if(std::begin(v), std::end(v),
                                        [&i](A & a){ return a.id() == i; });

            findItr->func();
        }
        auto tp0 = std::chrono::high_resolution_clock::now()- start;
        unsigned long long vTime = std::chrono::duration_cast<std::chrono::nanoseconds>(tp0).count();

        start = std::chrono::high_resolution_clock::now();
        for(unsigned i = 0; i < elementCount; ++i)
        {
            u[i].func();
        }
        auto tp1 = std::chrono::high_resolution_clock::now()- start;
        unsigned long long uTime = std::chrono::duration_cast<std::chrono::nanoseconds>(tp1).count();

        start = std::chrono::high_resolution_clock::now();
        for(unsigned i = 0; i < elementCount; ++i)
        {
            m[i].func();
        }
        auto tp2 = std::chrono::high_resolution_clock::now()- start;
        unsigned long long mTime = std::chrono::duration_cast<std::chrono::nanoseconds>(tp2).count();

        timesMap.insert(std::make_pair(elementCount ,Times{vTime, uTime, mTime}));
    }

    for(auto & itr : timesMap)
    {
        std::cout << "Element count: " << itr.first << std::endl; 
        std::cout << "std::vector time:        " << itr.second.v << std::endl;
        std::cout << "std::unordered_map time: " << itr.second.u << std::endl;
        std::cout << "std::map time:           " << itr.second.m << std::endl;
        std::cout << "-----------------------------------" << std::endl;
    }

    std::cout << dummy;
}

./lookup 
Element count: 10
std::vector time:        0
std::unordered_map time: 0
std::map time:           1000
-----------------------------------
Element count: 100
std::vector time:        0
std::unordered_map time: 3000
std::map time:           13000
-----------------------------------
Element count: 1000
std::vector time:        2000
std::unordered_map time: 29000
std::map time:           138000
-----------------------------------
Element count: 10000
std::vector time:        22000
std::unordered_map time: 287000
std::map time:           1610000
-----------------------------------
Element count: 100000
std::vector time:        72000
std::unordered_map time: 1539000
std::map time:           8994000
-----------------------------------
Element count: 1000000
std::vector time:        746000
std::unordered_map time: 12654000
std::map time:           154060000
-----------------------------------
Element count: 10000000
std::vector time:        8001000
std::unordered_map time: 123608000
std::map time:           2279362000
-----------------------------------
33333330