NAME¶

std::is_sorted - std::is_sorted

Synopsis¶

Defined in header <algorithm>
template< class ForwardIt > (since C++11)
bool is_sorted( ForwardIt first, ForwardIt last (until C++20)
);
template< class ForwardIt >
constexpr bool is_sorted( ForwardIt first, (since C++20)
ForwardIt last );
template< class ExecutionPolicy, class ForwardIt
> (2) (since C++17)
bool is_sorted( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last );
template< class ForwardIt, class Compare > (since C++11)
bool is_sorted( ForwardIt first, ForwardIt last, (1) (until C++20)
Compare comp );
template< class ForwardIt, class Compare >
constexpr bool is_sorted( ForwardIt first, (since C++20)
ForwardIt last, Compare comp );
template< class ExecutionPolicy, class (3)
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.

A sequence is sorted with respect to a comparator comp if for any iterator it
pointing to the sequence and any non-negative integer n such that it + n is a valid
iterator pointing to an element of the sequence, comp(*(it + n), *it) evaluates to
false.

1) Elements are compared using operator<.
3) Elements are compared using the given binary comparison function comp.
2,4) Same as (1,3), but executed according to policy. These overloads do not
participate in overload resolution unless
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) is true.

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.

Return value¶

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

Complexity¶

Linear in the distance between first and last.

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++.

First version¶

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

Second version¶

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 <iostream>
#include <algorithm>
#include <iterator>
int main()
{
int digits[] = {3, 1, 4, 1, 5};

for (auto i : digits) std::cout << i << ' ';
std::cout << ": is_sorted: " << std::boolalpha
<< std::is_sorted(std::begin(digits), std::end(digits)) << '\n';

std::sort(std::begin(digits), std::end(digits));

for (auto i : digits) std::cout << i << ' ';
std::cout << ": is_sorted: "
<< std::is_sorted(std::begin(digits), std::end(digits)) << '\n';
}

Output:¶

3 1 4 1 5 : is_sorted: false
1 1 3 4 5 : is_sorted: true

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)