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Searches the container for elements with a key equivalent to k and returns the number of matches.
Because all elements in a map container are unique, the function can only return 1 (if the element is found) or zero (otherwise).
Two keys are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the keys are passed as arguments).
Member type size_type is an unsigned integral type.
Output:
No mapped values are accessed: concurrently accessing or modifying elements is safe.
Reference
C library:
- <cassert> (assert.h)
- <cctype> (ctype.h)
- <cerrno> (errno.h)
-
<cfenv> (fenv.h)C++11
- <cfloat> (float.h)
-
<cinttypes> (inttypes.h)C++11
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
-
<cstdbool> (stdbool.h)C++11
- <cstddef> (stddef.h)
-
<cstdint> (stdint.h)C++11
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
-
<ctgmath> (tgmath.h)C++11
- <ctime> (time.h)
-
<cuchar> (uchar.h)C++11
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
-
<array>C++11
- <deque>
-
<forward_list>C++11
- <list>
- <map>
- <queue>
- <set>
- <stack>
-
<unordered_map>C++11
-
<unordered_set>C++11
- <vector>
-
Input/Output:
Multi-threading:
-
<atomic>C++11
-
<condition_variable>C++11
-
<future>C++11
-
<mutex>C++11
-
<thread>C++11
-
Other:
- <algorithm>
- <bitset>
-
<chrono>C++11
-
<codecvt>C++11
- <complex>
- <exception>
- <functional>
-
<initializer_list>C++11
- <iterator>
- <limits>
- <locale>
- <memory>
- <new>
- <numeric>
-
<random>C++11
-
<ratio>C++11
-
<regex>C++11
- <stdexcept>
- <string>
-
<system_error>C++11
-
<tuple>C++11
-
<type_traits>C++11
-
<typeindex>C++11
- <typeinfo>
- <utility>
- <valarray>
map
- map::~map
- map::map
member functions
-
map::atC++11
- map::begin
-
map::cbeginC++11
-
map::cendC++11
- map::clear
- map::count
-
map::crbeginC++11
-
map::crendC++11
-
map::emplaceC++11
-
map::emplace_hintC++11
- map::empty
- map::end
- map::equal_range
- map::erase
- map::find
- map::get_allocator
- map::insert
- map::key_comp
- map::lower_bound
- map::max_size
- map::operator[]
- map::operator=
- map::rbegin
- map::rend
- map::size
- map::swap
- map::upper_bound
- map::value_comp
-
non-member overloads
public member function
<map>
std::map::count
size_type count (const key_type& k) const;
Count elements with a specific key
Because all elements in a map container are unique, the function can only return 1 (if the element is found) or zero (otherwise).
Two keys are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the keys are passed as arguments).
Parameters
- k
- Key to search for.
Member type key_type is the type of the element keys in the container, defined in map as an alias of its first template parameter (Key).
Return value
1 if the container contains an element whose key is equivalent to k, or zero otherwise.Member type size_type is an unsigned integral type.
Example
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Output:
a is an element of mymap. b is not an element of mymap. c is an element of mymap. d is not an element of mymap. e is not an element of mymap. f is an element of mymap. g is not an element of mymap. |
Complexity
Logarithmic in size.Iterator validity
No changes.Data races
The container is accessed.No mapped values are accessed: concurrently accessing or modifying elements is safe.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container.See also
- map::find
- Get iterator to element (public member function)
- map::size
- Return container size (public member function)
- map::equal_range
- Get range of equal elements (public member function)
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Spotted an error? contact us