std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::contains
bool contains( const Key& key ) const; |
(1) | (since C++20) |
template< class K > bool contains( const K& x ) const; |
(2) | (since C++20) |
1) Checks if there is an element with key equivalent to
key
in the container.
2) Checks if there is an element with key that compares
equivalent to the value
x
. This overload participates in overload resolution only if
Hash::is_transparent
and
KeyEqual::is_transparent
are valid and each denotes a type. This assumes that such
Hash
is callable with both
K
and
Key
type, and that the
KeyEqual
is transparent, which, together, 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
true
if there is such an element, otherwise false
.
Complexity
Constant on average, worst case linear in the size of the container.
Example
#include <iostream> #include <unordered_map> int main() { std::unordered_map<int,char> example = {{1,'a'},{2,'b'}}; for(int x: {2, 5}) { if(example.contains(x)) { std::cout << x << ": Found\n"; } else { std::cout << x << ": Not found\n"; } } }
Output:
2: Found 5: Not found
See also
(C++11)
|
finds element with specific key (public member function) |
(C++11)
|
returns the number of elements matching specific key (public member function) |
(C++11)
|
returns range of elements matching a specific key (public member function) |
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