unordered_map::operator[]

Finds or inserts an element with the specified key.

Ty& operator[](const Key& keyval);

Parameters

• keyval
  The key value to find or insert.

Example

 

// std_tr1__unordered_map__unordered_map_operator_sub.cpp 
// compile with: /EHsc 
#include <unordered_map> 
#include <iostream> 
 
typedef std::tr1::unordered_map<char, int> Mymap; 
int main() 
    { 
    Mymap c1; 
 
    c1.insert(Mymap::value_type('a', 1)); 
    c1.insert(Mymap::value_type('b', 2)); 
    c1.insert(Mymap::value_type('c', 3)); 
 
// display contents " [c 3] [b 2] [a 1]" 
    for (Mymap::const_iterator it = c1.begin(); 
        it != c1.end(); ++it) 
        std::cout << " [" << it->first << ", " << it->second << "]"; 
    std::cout << std::endl; 
 
// try to find and fail 
    std::cout << "c1['A'] == " << c1['A'] << std::endl; 
 
// try to find and succeed 
    std::cout << "c1['a'] == " << c1['a'] << std::endl; 
 
// redisplay contents 
    for (Mymap::const_iterator it = c1.begin(); 
        it != c1.end(); ++it) 
        std::cout << " [" << it->first << ", " << it->second << "]"; 
    std::cout << std::endl; 
 
    return (0); 
    } 
 

[c, 3] [b, 2] [a, 1] c1['A'] == 0 c1['a'] == 1 [c, 3] [b, 2] [A, 0] [a, 1]

Remarks

The member function determines the iterator where as the return value of unordered_map::insert( unordered_map::value_type(keyval, Ty()). (It inserts an element with the specified key if no such element exists.) It then returns a reference to (*where).second.

Requirements

Header: <unordered_map>

Namespace: std::tr1

See Also

Reference

<unordered_map>

unordered_map Class

unordered_map::find

unordered_map::insert