c++ - 调用顺序引用一些信息

Question

现在我有 std::map<std::string, Object> myMap .类 Object具有以下功能:int getPriority()和 void Work() .现在我浏览 map 并想调用 Work由于对象的优先级。

我写了一个非常疯狂的想法:那个 map 的克隆，但它存储在它的优先级的键中，例如:

myMap["3_key1"] = Object();
myMap["6_key2"] = Object();
myMap["0_key3"] = Object();

它排序并且调用在正确的队列中:0_key3; 3_key1; 6_key2 .

但我认为这很慢。我想替换 std::map与 unordered_map来自 boost 因为它快了很多。并且没有按键排序。

那么，有什么想法吗？

Answer 1

使用Boost.MultiIndex :

// your class
#include <iostream>
#include <string>

class foo
{
public:
    foo(std::string name, unsigned priority, std::string msg) :
    mPriority(priority)
    {
        mName.swap(name); // primitive std::move :)
        mMsg.swap(msg); // (default-construct & swap)
    }

    const std::string& name() const
    {
        return mName;
    }

    unsigned priority() const
    {
        return mPriority;
    }

    void work() const
    {
        std::cout << mMsg << std::endl;
    }

private:
    std::string mName;

    unsigned mPriority;
    std::string mMsg;
};

// your container
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/mem_fun.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/sequenced_index.hpp>

namespace bmi = boost::multi_index;

typedef boost::multi_index_container<foo,
            bmi::indexed_by<
                // order by name (std::map)
                bmi::ordered_unique<
                    bmi::const_mem_fun<foo, const std::string&, &foo::name>
                        >,

                // order by priority (std::multi_map)
                bmi:: ordered_non_unique<
                    bmi::const_mem_fun<foo, unsigned ,&foo::priority>
                        >
                > 
            > foo_set;

// test
#include <boost/foreach.hpp>

int main()
{
    foo_set fooSet;
    fooSet.insert(foo("a", 4, "this is a, priority 4"));
    fooSet.insert(foo("b", 3, "this is b, priority 3"));
    fooSet.insert(foo("c", 7, "this is c, priority 7"));
    fooSet.insert(foo("d", 1, "this is c, priority 1"));

    // view as map from name to value
    foo_set::nth_index<0>::type& nameView = fooSet.get<0>();

    nameView.find("a")->work(); // find "a", print its message
    if (nameView.find("e") == nameView.end())
        std::cerr << "e not found" << std::endl;

    std::cout << std::endl;

    // view as multi_map from priority to value
    foo_set::nth_index<1>::type& priorityView = fooSet.get<1>();

    BOOST_FOREACH(const foo& f, priorityView)
        f.work(); // work, in order of priority
}

我没有对其进行任何性能测试，但它肯定能更好地表达您的意图，而且这通常表明性能有所提高。