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Returns a copy of the comparison object used by the container.
By default, this is a less object, which returns the same as operator<.
This object determines the order of the elements in the container: it is a function pointer or a function object that takes two arguments of the same type as the container elements, and returns true if the first argument is considered to go before the second in the strict weak ordering it defines, and false otherwise.
Two elements of a set are considered equivalent if key_comp returns false reflexively (i.e., no matter the order in which the elements are passed as arguments).
In set containers, the keys to sort the elements are the values themselves, therefore key_comp and its sibling member function value_comp are equivalent.
Member type key_compare is the type of the comparison object associated to the container, defined in set as an alias of its second template parameter (Compare).
Output:
Concurrently accessing the elements of a set 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>
set
- set::~set
- set::set
member functions
- set::begin
-
set::cbeginC++11
-
set::cendC++11
- set::clear
- set::count
-
set::crbeginC++11
-
set::crendC++11
-
set::emplaceC++11
-
set::emplace_hintC++11
- set::empty
- set::end
- set::equal_range
- set::erase
- set::find
- set::get_allocator
- set::insert
- set::key_comp
- set::lower_bound
- set::max_size
- set::operator=
- set::rbegin
- set::rend
- set::size
- set::swap
- set::upper_bound
- set::value_comp
non-member overloads
public member function
<set>
std::set::key_comp
key_compare key_comp() const;
Return comparison object
By default, this is a less object, which returns the same as operator<.
This object determines the order of the elements in the container: it is a function pointer or a function object that takes two arguments of the same type as the container elements, and returns true if the first argument is considered to go before the second in the strict weak ordering it defines, and false otherwise.
Two elements of a set are considered equivalent if key_comp returns false reflexively (i.e., no matter the order in which the elements are passed as arguments).
In set containers, the keys to sort the elements are the values themselves, therefore key_comp and its sibling member function value_comp are equivalent.
Parameters
noneReturn value
The comparison object.Member type key_compare is the type of the comparison object associated to the container, defined in set as an alias of its second template parameter (Compare).
Example
|
|
Output:
myset contains: 0 1 2 3 4 |
Complexity
Constant.Iterator validity
No changes.Data races
The container is accessed.Concurrently accessing the elements of a set is safe.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container.See also
- set::value_comp
- Return comparison object (public member function)
- set::find
- Get iterator to element (public member function)
- set::count
- Count elements with a specific value (public member function)
- set::lower_bound
- Return iterator to lower bound (public member function)
- set::upper_bound
- Return iterator to upper bound (public member function)
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Spotted an error? contact us