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std::map::find

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< cpp‎ | container‎ | map
Revision as of 10:32, 19 September 2013 by Nate (Talk | contribs)

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iterator find( const Key& key );
(1)
const_iterator find( const Key& key ) const;
(2)
template< class K > iterator find( const K& x );
(3) (since C++14)
template< class K > const_iterator find( const K& x ) const;
(4) (since C++14)
1,2) Finds an element with key equivalent to key.
3,4) Finds an element with key that compares equivalent to the value x. These templates only participate in overload resolution if the type Compare::is_transparent exists. They allow calling this function without constructing an instance of Key

Contents

[edit] Parameters

key - key value of the element to search for
x - a value of any type that can be transparently compared with a key

[edit] Return value

Iterator to an element with key equivalent to key. If no such element is found, past-the-end (see end()) iterator is returned.

[edit] Complexity

Logarithmic in the size of the container.

[edit] Example

#include <iostream>
#include <map>
 
int main()
{  
    std::map<int,char> example = {{1,'a'},{2,'b'}};
 
    auto search = example.find(2);
    if(search != example.end()) {
        std::cout << "Found " << search->first << " " << search->second << '\n';
    }
    else {
        std::cout << "Not found\n";
    }
}

Output:

Found 2 b

[edit] See also

returns the number of elements matching specific key
(public member function) [edit]
returns range of elements matching a specific key
(public member function) [edit]


[edit] Example

Demonstrates the risk of accessing non-existing elements via operator [].

#include <string>
#include <iostream>
#include <map>
 
int main()
{
    std::map<std::string,int> my_map;
    my_map["x"] =  11;
    my_map["y"] = 23;
 
    auto it = my_map.find("x");
    if (it != my_map.end()) std::cout << "x: " << it->second << "\n";
 
    it = my_map.find("z");
    if (it != my_map.end()) std::cout << "z1: " << it->second << "\n";
 
    // Accessing a non-existing element creates it
    if (my_map["z"] == 42) std::cout << "Oha!\n";
 
    it = my_map.find("z");
    if (it != my_map.end()) std::cout << "z2: " << it->second << "\n";
}

Output:

x: 11
z2: 0