[STL] C++ STL map

C++ map

map을 사용하기 위해서는 <map 헤더를 인클루드 해야한다.

key와 value를 쌍으로 저장한다.

set과 마찬가지로 key를 중복으로 저장할 수 없으며, 중복된 key를 이용하려면 multimap을 이용하면 된다.

map은 []연산자를 이용하여 key에 접근할 수 있다.

map은 pair객체로 원소를 저장하기 때문에, 첫번째 key는 first로 두번째 value는 second로 접근할 수 있다.

생성자 사용 예제

#include <iostream>
#include <map>
#include <functional>
 
int main()
{
    std::map<char, int> first;
 
    first['a'] = 10;
    first['b'] = 30;
    first['c'] = 50;
    first['d'] = 70;
 
    std::map<char, int> second(first.begin(), first.end());
 
    std::map<char, int> third(second);
 
    std::map<char, int, std::greater<int> > fourth = { {'a', 10}, {'b', 30}, {'c', 50}, {'d', 70} }; 
 
    std::cout << "first : ";
    for (auto it = first.begin(); it != first.end(); it++)
        std::cout << (*it).first << ' ' << (*it).second << ' ';
    std::cout << '\n';
 
    std::cout << "second : ";
    for (auto it = second.begin(); it != second.end(); it++)
        std::cout << (*it).first << ' ' << (*it).second << ' ';
    std::cout << '\n';
 
    std::cout << "third : ";
    for (auto it = third.begin(); it != third.end(); it++)
        std::cout << (*it).first << ' ' << (*it).second << ' ';
    std::cout << '\n';
 
    std::cout << "fourth : ";
    for (auto it = fourth.begin(); it != fourth.end(); it++)
        std::cout << (*it).first << ' ' << (*it).second << ' ';
    std::cout << '\n';
 
    return 0;
}

실행 결과

멤버함수 사용 예제

insert()

#include <iostream>
#include <map>
 
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;
}

find(), erase()

#include <iostream>
#include <map>
 
int main ()
{
  std::map<char,int> mymap;
  std::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)
    std::cout << it->first << " => " << it->second << '\n';
 
  return 0;
}

count()

#include <iostream>
#include <map>
 
int main ()
{
  std::map<char,int> mymap;
  char c;
 
  mymap ['a']=101;
  mymap ['c']=202;
  mymap ['f']=303;
 
  for (c='a'; c<'h'; c++)
  {
    std::cout << c;
    if (mymap.count(c)>0)
      std::cout << " is an element of mymap.\n";
    else 
      std::cout << " is not an element of mymap.\n";
  }
 
  return 0;
}

참조: http://www.cplusplus.com/reference/map/map/

참고문헌: 뇌를 자극하는 C++ STL