std::map 排序规则研究

 

struct C_S
{
 int m_a;
 std::string m_s;
 
 C_S(const std::string &s,int i):m_a(i),m_s(s)
 {
  //
 }

 //重载operator<,支持
 //std::map<C_S,int>这类默认定义,实际
 //是std::map<C_S,int,std::less<C_S> >;
 bool operator<(const C_S &c_s) const
 {
  return c_s.m_a > this->m_a;
 }

 //重载operator>,支持
 //std::map<C_S,int,std::greater<C_S> >
 //指定map按key 从大到小排序
 bool operator>(const C_S &c_s) const
 {
  return c_s.m_a < this->m_a;
 }

 //bool operator!(const C_S &c_s) const
 //{
  //return c_s.m_a == this->m_a && c_s.m_s == this->m_s;
 //}
};

void map_test()
{
 //MAP 元素按从大大小的顺序排列
 std::map<C_S,int> less_map; 
 less_map[C_S("AAA",3)] = 3; 
 less_map[C_S("BBB",1)] = 1;
 less_map[C_S("CCC",2)] = 2;
 std::map<C_S,int,std::less<C_S>>::iterator it;
 std::cout<<"MAP less rule:"<<endl;
 for(it = less_map.begin();it != less_map.end();++it)
 {
  std::cout<<it->second<<":"<<it->first.m_a<<endl;
 }
 std::cout<<endl;
 
 //MAP 元素按从大大小的顺序排列
 std::map<C_S,int,std::greater<C_S> > greater_m; 
 greater_m[C_S("AAA",3)] = 3; 
 greater_m[C_S("BBB",1)] = 1;
 greater_m[C_S("CCC",2)] = 2;
 std::map<C_S,int,std::greater<C_S>>::iterator map_it;
 std::cout<<"MAP greater rule:"<<endl;
 for(map_it = greater_m.begin();map_it != greater_m.end();++map_it)
 {
  std::cout<<map_it->second<<":"<<map_it->first.m_a<<endl;
 }
}

//去处 multimap 里面重复数据的方法
int main(int argc,char *argv[])
{
 
 map_test(); 

}