template< class ForwardIt >
bool is_sorted( ForwardIt first, ForwardIt last );
(1)
(since C++11) (constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt >
bool is_sorted( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last );
(2)
(since C++17)
template< class ForwardIt, class Compare >
bool is_sorted( ForwardIt first, ForwardIt last, Compare comp );
(3)
(since C++11) (constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt, class Compare >
bool is_sorted( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last, Compare comp );
(4)
(since C++17)
Checks if the elements in range [first, last) are sorted in non-descending order.
1) Checks if the elements are
sorted with respect to
operator<(until C++20)std::less {}(since C++20).
3) Checks if the elements are sorted with respect to comp.
2,4) Same as (1,3), but executed according to policy.
These overloads participate in overload resolution only if all following conditions are satisfied:
[edit] Parameters
first, last
-
the pair of iterators defining the
range of elements to examine
comp
-
comparison function object (i.e. an object that satisfies the requirements of
Compare) which returns
true if the first argument is
less than (i.e. is ordered
before) the second.
The signature of the comparison function should be equivalent to the following:
bool cmp(const Type1& a, const Type2& b);
While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1& is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy(since C++11)).
The types Type1 and Type2 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to both of them.
Type requirements
-
Compare must meet the requirements of
Compare.
[edit] Return value
true if the elements in the range are sorted in non-descending order, false otherwise.
[edit] Complexity
Given \(\scriptsize N\)N as std::distance (first, last):
1,2) \(\scriptsize O(N)\)O(N) comparisons using
operator<(until C++20)std::less {}(since C++20).
3,4) \(\scriptsize O(N)\)O(N) applications of the comparator comp.
[edit] Exceptions
The overloads with a template parameter named ExecutionPolicy report errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
- If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] Possible implementation
See also the implementations in libstdc++ and libc++.
std::is_sorted returns true for empty ranges and ranges of length one.
[edit] Example
#include <algorithm>
#include <cassert>
#include <functional>
#include <iterator>
#include <vector>
int main()
{
std::vector <int> v;
assert (std::is_sorted(v.cbegin(), v.cend()) && "an empty range is always sorted");
v.push_back(42);
assert (std::is_sorted(v.cbegin(), v.cend()) && "a range of size 1 is always sorted");
int data[] = {3, 1, 4, 1, 5};
assert (not std::is_sorted(std::begin (data), std::end (data)));
std::sort (std::begin (data), std::end (data));
assert (std::is_sorted(std::begin (data), std::end (data)));
assert (not std::is_sorted(std::begin (data), std::end (data), std::greater <>{}));
}
[edit] See also
finds the largest sorted subrange
(function template) [edit]
checks whether a range is sorted into ascending order
(algorithm function object)[edit]