std::map::find

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

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)

Technical Specifications

 

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

queue

priority_queue

 

std::map

Member functions

map::map

map::~map

map::operator=

map::get_allocator

Element access

map::at

map::operator[]

Iterators

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

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

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

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

Capacity

map::empty

map::size

map::max_size

Modifiers

map::clear

map::insert

map::insert_or_assign (C++17)

map::emplace (C++11)

map::emplace_hint (C++11)

map::try_emplace (C++17)

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 );	(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. This overload only participates in overload resolution if the qualified-id Compare::is_transparent is valid and denotes a type. It allows calling this function without constructing an instance of Key

Parameters

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

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.

Complexity

Logarithmic in the size of the container.

Example

Run this code

#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

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()
{
    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