C++ map insert 另一个map的子集

C++map中 会有insert操作，举个例子

存在map A，我们截取一部分到map B中，void insert (InputIterator first, InputIterator last) ，截取的部分是 first 到 last 前一个迭代器的值

// map::insert (C++98)
#include <iostream>
#include <map>

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

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

  std::pair<std::map<char,int>::iterator,bool> ret;
  ret = mymap.insert ( std::pair<char,int>('z',) );
  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',));  // max efficiency inserting
  mymap.insert (it, std::pair<char,int>('c',));  // 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 ;
}

输出结果：

element 'z' already existed with a value of
mymap contains:
a =>
b =>
c =>
z =>
anothermap contains:
a =>
b => 

详细信息可参考:  http://www.cplusplus.com/reference/map/map/insert/