std::is_sorted

Since C++17

Header: <algorithm>

Checks if the elements in range [first,last) are sorted in non-descending order.

# Declarations

template< class ForwardIt >
bool is_sorted( ForwardIt first, ForwardIt last );

(since C++11) (constexpr since C++20)

template< class ExecutionPolicy, class ForwardIt >
bool is_sorted( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last );

(since C++17)

template< class ForwardIt, class Compare >
bool is_sorted( ForwardIt first, ForwardIt last, Compare comp );

(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 );

(since C++17)

# Parameters

first, last: the range of elements to examine
policy: the execution policy to use
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.

# Return value

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

# Notes

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

# 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<>{}));
}