std::map::find

 

C++

Language

Standard library headers

Concepts

Utilities library

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Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Containers library

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

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std::map

Member functions

map::map

map::~map

map::operator=

map::get_allocator

Element access

map::at

map::operator[]

Iterators

map::begin map::cbegin (C++11)

map::end map::cend (C++11)

map::rbegin map::crbegin (C++11)

map::rend map::crend (C++11)

Capacity

map::empty

map::size

map::max_size

Modifiers

map::clear

map::insert

map::emplace (C++11)

map::emplace_hint (C++11)

map::erase

map::swap

Lookup

map::count

map::find

map::equal_range

map::lower_bound

map::upper_bound

Observers

map::key_comp

map::value_comp

 

iterator find( const Key& key );
const_iterator find( const Key& key ) const;

Finds an element with key key.

Parameters

key

-

key value of the element to search for

Return value

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

Complexity

Logarithmic in the size of the container.

See also

count	returns the number of elements matching specific key (public member function)
equal_range	returns range of elements matching a specific key (public member function)

Example

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

run this code

#include <string>
#include <iostream>
#include <map>
 
int main()
{
    typedef std::map<std::string,int>  mapT;
 
    mapT my_map;
    my_map["x"]=  11;
    my_map["y"]= 23;
 
    mapT::iterator  it= my_map.find("x");
    if( it != my_map.end() ) std::cout << "A: " << it->second << "\n";
 
    it= my_map.find("z");
    if( it != my_map.end() ) std::cout << "B: " << 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 << "C: " << it->second << "\n";
 
    return 0;
}

Output:

A: 11
C: 0