NAME¶

std::is_sorted - std::is_sorted

Synopsis¶

Defined in header <algorithm>
template< class ForwardIt > (1) (since C++11)
bool is_sorted( ForwardIt first, ForwardIt last ); (constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt >

bool is_sorted( ExecutionPolicy&& policy, (2) (since C++17)

ForwardIt first, ForwardIt last );
template< class ForwardIt, class Compare > (since C++11)
bool is_sorted( ForwardIt first, ForwardIt last, Compare (3) (constexpr since C++20)
comp );
template< class ExecutionPolicy, class ForwardIt, class
Compare >

bool is_sorted( ExecutionPolicy&& policy, (4) (since C++17)

ForwardIt first, ForwardIt last, Compare
comp );

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

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. (until
C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. (since
C++20)

Parameters¶

first, last - the range of elements to examine
policy - the execution policy to use. See execution policy for details.
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);
comp -
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¶

-
ForwardIt must meet the requirements of LegacyForwardIterator.
-
Compare must meet the requirements of Compare.

Return value¶

true if the elements in the range are sorted in non-descending order, false
otherwise.

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.

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.

Possible implementation¶

See also the implementations in libstdc++ and libc++.

is_sorted (1)
template<class ForwardIt>
bool is_sorted(ForwardIt first, ForwardIt last)
{
return std::is_sorted_until(first, last) == last;
}
is_sorted (3)
template<class ForwardIt, class Compare>
bool is_sorted(ForwardIt first, ForwardIt last, Compare comp)
{
return std::is_sorted_until(first, last, comp) == last;
}

Notes¶

std::is_sorted returns true for empty ranges and ranges of length one.

Example¶

// Run this code

#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<>{}));
}

See also¶

is_sorted_until finds the largest sorted subrange
(C++11) (function template)
ranges::is_sorted checks whether a range is sorted into ascending order
(C++20) (niebloid)