std::unordered_map<Key,T,Hash,KeyEqual,Allocator>:: contains
From cppreference.com
<
cpp
|
container
|
unordered map
|
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
Run this code
#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
|
finds element with specific key
(public member function) |
|
|
returns the number of elements matching specific key
(public member function) |
|
|
returns range of elements matching a specific key
(public member function) |