unordered_map是采用哈希搜索的map。搜索速度上也许要优于map。

需要主意的是，对map对象进行遍历时，该对象有可能是未排序的。

源程序如下：

/* B00011 unordered_map */

#include <iostream>
#include <string>
#include <unordered_map>

using namespace std;

int main()
{
    // Create an unordered_map of three strings (that map to strings)
    std::unordered_map<std::string, std::string> u = {
        {"RED","#FF0000"},
        {"GREEN","#00FF00"},
        {"BLUE","#0000FF"}
    };

    // Iterate and print keys and values of unordered_map
    for( const auto& n : u ) {
        std::cout << "Key:[" << n.first << "] Value:[" << n.second << "]\n";
    }

    // Add two new entries to the unordered_map
    u["BLACK"] = "#000000";
    u["WHITE"] = "#FFFFFF";

    // Output values by key
    std::cout << "The HEX of color RED is:[" << u["RED"] << "]\n";
    std::cout << "The HEX of color BLACK is:[" << u["BLACK"] << "]\n";

    return 0;
}


程序运行结果如下：

Key:[BLUE] Value:[#0000FF]

Key:[RED] Value:[#FF0000]

Key:[GREEN] Value:[#00FF00]

The HEX of color RED is:[#FF0000]

The HEX of color BLACK is:[#000000]