# C++ Algorithm Library - is_sorted_until() Function

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## Description

The C++ function std::algorithm::is_sorted_until() finds first unsorted element from the sequence. It uses binary function for comparison.

## Declaration

Following is the declaration for std::algorithm::is_sorted_until() function form std::algorithm header.

### C++11

```template <class ForwardIterator, class Compare>
ForwardIterator is_sorted_until(ForwardIterator first, ForwardIterator last,
Compare comp);
```

## Parameters

• first − Forward iterator to the initial position.

• last − Forward iterator to the final position.

• comp − A binary function which accepts two arguments and returns bool.

## Return value

Returns an iterator to the first unsorted element. If entire range is sorted then it returns last.

## Exceptions

Throws exception if either the binary function or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

Linear.

## Example

The following example shows the usage of std::algorithm::is_sorted_until() function.

```#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

bool ignore_case(char a, char b) {
return (tolower(a) == tolower(b));
}

int main(void) {
vector<char> v = {'A', 'b', 'C', 'd', 'E'};

auto it = is_sorted_until(v.begin(), v.end());

cout << "First unsorted element = " << *it << endl;

it = is_sorted_until(v.begin(), v.end(), ignore_case);

if (it == end(v))
cout << "Entire vector is sorted." << endl;

return 0;
}
```

Let us compile and run the above program, this will produce the following result −

```First unsorted element = C
Entire vector is sorted.
```
algorithm.htm