map常用操作

初始化和赋值

// constructing maps
#include <iostream>
#include <map>
using namespace std;

bool fncomp (char lhs, char rhs) {return lhs<rhs;}

struct classcomp {
  bool operator() (const char& lhs, const char& rhs) const
  {return lhs<rhs;}
};

int main ()
{
  map<char,int> first;

  first['a']=10;
  first['b']=30;
  first['c']=50;
  first['d']=70;

  map<char,int> second (first.begin(),first.end());

  map<char,int> third (second);

  map<char,int,classcomp> fourth;                 // class as Compare

  bool(*fn_pt)(char,char) = fncomp;
  map<char,int,bool(*)(char,char)> fifth (fn_pt); // function pointer as Compare

  return 0;
}

 如果map::operator[]中key不匹配任何在容器中的元素，该函数插入一个新元素,元素是使用其默认构造函数构造。

 

获取元素数量

// map::size
#include <iostream>
#include <map>
using namespace std;

int main ()
{
  map<char,int> mymap;
  mymap['a']=101;
  mymap['b']=202;
  mymap['c']=302;

  cout << "mymap.size() is " << (int) mymap.size() << endl;

  return 0;
}

 

// map::empty
#include <iostream>
#include <map>
using namespace std;

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

  mymap['a']=10;
  mymap['b']=20;
  mymap['c']=30;

  while (!mymap.empty())
  {
     cout << mymap.begin()->first << " => ";
     cout << mymap.begin()->second << endl;
     mymap.erase(mymap.begin());
  }

  return 0;
}

 

插入

// map::insert
#include <iostream>
#include <map>
using namespace std;

int main ()
{
  map<char,int> mymap;
  map<char,int>::iterator it;
  pair<map<char,int>::iterator,bool> ret;

  // first insert function version (single parameter):
  mymap.insert ( pair<char,int>('a',100) );
  mymap.insert ( pair<char,int>('z',200) );
  ret=mymap.insert (pair<char,int>('z',500) ); 
  if (ret.second==false)
  {
    cout << "element 'z' already existed";
    cout << " with a value of " << ret.first->second << endl;
  }

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

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

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

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

  return 0;
}

 

遍历

// map::begin/end
#include <iostream>
#include <map>
using namespace std;

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

  mymap['b'] = 100;
  mymap['a'] = 200;
  mymap['c'] = 300;

  // show content:
  for ( it=mymap.begin() ; it != mymap.end(); it++ )
    cout << (*it).first << " => " << (*it).second << endl;

  return 0;
}

 

查找

// map::find
#include <iostream>
#include <map>
using namespace std;

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

  mymap['a']=50;
  mymap['b']=100;
  mymap['c']=150;
  mymap['d']=200;

  it=mymap.find('b');
  mymap.erase (it);
  mymap.erase (mymap.find('d'));
  it=mymap.find('d');
  if (it == mymap.end()) {
      cout << "key 'd' is not exist" << endl;
  }
  // print content:
  cout << "elements in mymap:" << endl;
  cout << "a => " << mymap.find('a')->second << endl;
  cout << "c => " << mymap.find('c')->second << endl;

  return 0;
}

 

删除

// erasing from map
#include <iostream>
#include <map>
using namespace std;

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

  // insert some values:
  mymap['a']=10;
  mymap['b']=20;
  mymap['c']=30;
  mymap['d']=40;
  mymap['e']=50;
  mymap['f']=60;

  it=mymap.find('b');
  mymap.erase (it);                   // erasing by iterator

  mymap.erase ('c');                  // erasing by key

  it=mymap.find ('e');
  mymap.erase ( it, mymap.end() );    // erasing by range

  // show content:
  for ( it=mymap.begin() ; it != mymap.end(); it++ )
    cout << (*it).first << " => " << (*it).second << endl;

  return 0;
}

 

更多操作

 参考  http://www.cplusplus.com/reference/stl/map/empty/