map::const_reference
A type that provides a reference to a const element stored in a map for reading and performing const operations.
typedef typename allocator_type::const_reference const_reference;
Example
// map_const_ref.cpp
// compile with: /EHsc
#include <map>
#include <iostream>
int main( )
{
using namespace std;
map <int, int> m1;
typedef pair <int, int> Int_Pair;
m1.insert ( Int_Pair ( 1, 10 ) );
m1.insert ( Int_Pair ( 2, 20 ) );
// Declare and initialize a const_reference &Ref1
// to the key of the first element
const int &Ref1 = ( m1.begin( ) -> first );
// The following line would cause an error as the
// non-const_reference cannot be used to access the key
// int &Ref1 = ( m1.begin( ) -> first );
cout << "The key of first element in the map is "
<< Ref1 << "." << endl;
// Declare and initialize a reference &Ref2
// to the data value of the first element
int &Ref2 = ( m1.begin( ) -> second );
cout << "The data value of first element in the map is "
<< Ref2 << "." << endl;
}
The key of first element in the map is 1.
The data value of first element in the map is 10.
Requirements
Header: <map>
Namespace: std