C++ STL map key是自定义结构体或类

/// @file 1.cpp
/// @brief
/// @author EastonWoo
/// 0.01
/// @date 2015-11-02

#include <stdio.h>
#include <unistd.h>
#include <semaphore.h>
#include <pthread.h>

#include <string>
#include <map>

class CKey{
public:
CKey(std::string str1, std::string str2) {
this->str1 = str1;
this->str2 = str2;
}
public:
std::string str1;
std::string str2;

public:
bool operator<(const CKey & ct) const   // 两个const是必需的。
{
if (str1 < ct.str1) {
return true;
} else if (str1 == ct.str1) {
if ( str2 < ct.str2 ) {
return true;
}
}

return false;
}
};

int main(int argc, const char *argv[])
{
std::map<CKey, std::string> _map;

CKey key1("11", "12");  // 被key6覆盖
CKey key6("11", "12");
CKey key5("23", "12");
CKey key7("22", "22");
CKey key2("21", "22");
CKey key3("21", "23");
CKey key4("21", "21");

_map[key1] = "hello";
_map[key2] = "world1";
_map[key3] = "world2";
_map[key4] = "world3";
_map[key5] = "world4";
_map[key6] = "world5";
_map[key7] = "world6";

for(auto it = _map.begin(); it != _map.end(); ++it) {
printf("[%s:%s]it->second = %s\n", it->first.str1.c_str(), it->first.str2.c_str(), it->second.c_str());
}

return 0;
}

// 编译,打印
// tmp-> g++ 1.cpp -std=c++0x && ./a.out
// [11:12]it->second = world5
// [21:21]it->second = world3
// [21:22]it->second = world1
// [21:23]it->second = world2
// [22:22]it->second = world6
// [23:12]it->second = world4
// tmp->
//
//
// 结果： key5 > key7 > key3 > key2 > key4 > key6 = key1
//                                           key1 被 key6 覆盖