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
#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
| returns the number of elements matching specific key (public member function) | |
| returns range of elements matching a specific key (public member function) |
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
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