C++ map insert 返回值 pair

// map::insert (C++98)
#include 
#include 

int main ()
{
  std::map<char,int> mymap;

  // first insert function version (single parameter):
  mymap.insert ( std::pair<char,int>('a',100) );
  mymap.insert ( std::pair<char,int>('z',200) );

  std::pair<std::map<char,int>::iterator,bool> ret;
  ret = mymap.insert ( std::pair<char,int>('z',500) );
  if (ret.second==false) {
    std::cout << "element 'z' already existed";
    std::cout << " with a value of " << ret.first->second << '\n';
  }

  // second insert function version (with hint position):
  std::map<char,int>::iterator it = mymap.begin();
  mymap.insert (it, std::pair<char,int>('b',300));  // max efficiency inserting
  mymap.insert (it, std::pair<char,int>('c',400));  // no max efficiency inserting

  // third insert function version (range insertion):
  std::map<char,int> anothermap;
  anothermap.insert(mymap.begin(),mymap.find('c'));

  // showing contents:
  std::cout << "mymap contains:\n";
  for (it=mymap.begin(); it!=mymap.end(); ++it)
    std::cout << it->first << " => " << it->second << '\n';

  std::cout << "anothermap contains:\n";
  for (it=anothermap.begin(); it!=anothermap.end(); ++it)
    std::cout << it->first << " => " << it->second << '\n';

  return 0;
}

例子

#include
#include
#include

using namespace std;

int main()
{
        std::map<char,int> mymap;
         mymap.insert ( std::pair<char,int>('a',100) );
         mymap.insert ( std::pair<char,int>('z',200) );
        std::pair<std::map<char,int>::iterator,bool> ret;

        //更改值
        ret = mymap.insert(std::pair<char,int>('z',500));

        cout<<ret.first->second<<endl;

        ret.first->second = 500;

        cout<<ret.first->second<<endl;

        //插入新值:已经创建节点
        ret = mymap.insert(std::pair<char,int>('b',500));
        ret.first->second=120;

        cout<<mymap['b']<<endl;
}

结果
200
500
120