hash_map::operator[]
참고
이 API는 사용되지 않습니다.unordered_map 클래스를 대신 사용하는 것이 좋습니다.
지정된 키 값을 사용하여 hash_map에 요소를 삽입합니다.
Type& operator[](
const Key& _Key
);
Type& operator[](
Key&& _Key
);
매개 변수
Parameter |
설명 |
_Key |
The key value of the element that is to be inserted. |
반환 값
A reference to the data value of the inserted element.
설명
If the argument key value is not found, then it is inserted along with the default value of the data type.
operator[] may be used to insert elements into a hash_map m using
m[_Key] = DataValue;
where DataValue is the value of the mapped_type of the element with a key value of _Key.
When using operator[] to insert elements, the returned reference does not indicate whether an insertion is changing a preexisting element or creating a new one. The member functions find and insert can be used to determine whether an element with a specified key is already present before an insertion.
예제
// hash_map_op_ref.cpp
// compile with: /EHsc
#include <hash_map>
#include <iostream>
#include <string>
int main( )
{
using namespace std;
using namespace stdext;
typedef pair <const int, int> cInt2Int;
hash_map <int, int> hm1;
hash_map <int, int> :: iterator pIter;
// Insert a data value of 10 with a key of 1
// into a hash_map using the operator[] member function
hm1[ 1 ] = 10;
// Compare other ways to insert objects into a hash_map
hm1.insert ( hash_map <int, int> :: value_type ( 2, 20 ) );
hm1.insert ( cInt2Int ( 3, 30 ) );
cout << "The keys of the mapped elements are:";
for ( pIter = hm1.begin( ) ; pIter != hm1.end( ) ; pIter++ )
cout << " " << pIter -> first;
cout << "." << endl;
cout << "The values of the mapped elements are:";
for ( pIter = hm1.begin( ) ; pIter != hm1.end( ) ; pIter++ )
cout << " " << pIter -> second;
cout << "." << endl;
// If the key already exists, operator[]
// changes the value of the datum in the element
hm1[ 2 ] = 40;
// operator[] will also insert the value of the data
// type's default constructor if the value is unspecified
hm1[5];
cout << "The keys of the mapped elements are now:";
for ( pIter = hm1.begin( ) ; pIter != hm1.end( ) ; pIter++ )
cout << " " << pIter -> first;
cout << "." << endl;
cout << "The values of the mapped elements are now:";
for ( pIter = hm1.begin( ) ; pIter != hm1.end( ) ; pIter++ )
cout << " " << pIter -> second;
cout << "." << endl;
// opperator[] will also insert by moving a key
hash_map <string, int> hm2;
string str("a");
hm2[move(str)] = 1;
cout << "The moved key is " << hm2.begin()->first
<< ", with value " << hm2.begin()->second << endl;
}
Output
The keys of the mapped elements are: 1 2 3.
The values of the mapped elements are: 10 20 30.
The keys of the mapped elements are now: 1 2 3 5.
The values of the mapped elements are now: 10 40 30 0.
The moved key is a, with value 1.
요구 사항
헤더: <hash_map>
네임스페이스: stdext