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