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Returns a comparison object that can be used to compare two elements to get whether the key of the first one goes before the second.
The arguments taken by this function object are of member type value_type (defined in map as an alias of pair<const key_type,mapped_type>), but the mapped_type part of the value is not taken into consideration in this comparison.
The comparison object returned is an object of the member type map::value_compare, which is a nested class that uses the internal comparison object to generate the appropriate comparison functional class. It is defined with the same behavior as:
The public member of this comparison class returns true if the key of the first argument is considered to go before that of the second (according to the strict weak ordering specified by the container's comparison object, key_comp), and false otherwise.
Notice that value_compare has no public constructor, therefore no objects can be directly created from this nested class outside map members.
Member type value_compare is a nested class type (described above).
Output:
No contained elements are accessed: concurrently accessing or modifying them 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::value_comp
value_compare value_comp() const;
Return value comparison object
The arguments taken by this function object are of member type value_type (defined in map as an alias of pair<const key_type,mapped_type>), but the mapped_type part of the value is not taken into consideration in this comparison.
The comparison object returned is an object of the member type map::value_compare, which is a nested class that uses the internal comparison object to generate the appropriate comparison functional class. It is defined with the same behavior as:
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The public member of this comparison class returns true if the key of the first argument is considered to go before that of the second (according to the strict weak ordering specified by the container's comparison object, key_comp), and false otherwise.
Notice that value_compare has no public constructor, therefore no objects can be directly created from this nested class outside map members.
Parameters
noneReturn value
The comparison object for element values.Member type value_compare is a nested class type (described above).
Example
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Output:
mymap contains: x => 1001 y => 2002 z => 3003 |
Complexity
Constant.Iterator validity
No changes.Data races
The container is accessed.No contained elements are accessed: concurrently accessing or modifying them is safe.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container.See also
- map::key_comp
- Return key comparison object (public member function)
- map::find
- Get iterator to element (public member function)
- map::count
- Count elements with a specific key (public member function)
- map::lower_bound
- Return iterator to lower bound (public member function)
- map::upper_bound
- Return iterator to upper bound (public member function)
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Spotted an error? contact us