std::unique_copy

template< class InputIt, class OutputIt >
OutputIt unique_copy( InputIt first, InputIt last, OutputIt d_first );

template< class InputIt, class OutputIt >
constexpr OutputIt unique_copy( InputIt first, InputIt last, OutputIt d_first );

template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 >
ForwardIt2 unique_copy( ExecutionPolicy&& policy, ForwardIt1 first,
                        ForwardIt1 last, ForwardIt2 d_first );

template< class InputIt, class OutputIt, class BinaryPredicate >
OutputIt unique_copy( InputIt first, InputIt last,
                      OutputIt d_first, BinaryPredicate p );

template< class InputIt, class OutputIt, class BinaryPredicate >
constexpr OutputIt unique_copy( InputIt first, InputIt last,
                                OutputIt d_first, BinaryPredicate p );

template< class ExecutionPolicy, class ForwardIt1,
          class ForwardIt2, class BinaryPredicate >
ForwardIt2 unique_copy( ExecutionPolicy&& policy,
                        ForwardIt1 first, ForwardIt1 last,
                        ForwardIt2 d_first, BinaryPredicate p );

Copies the elements from the range [first, last), to another range beginning at d_first in such a way that there are no consecutive equal elements. Only the first element of each group of equal elements is copied.

Parameters

Return value

Output iterator to the element past the last written element.

Complexity

For nonempty ranges, exactly std::distance(first, last) - 1 applications of the corresponding predicate.

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.

Notes

If InputIt satisfies LegacyForwardIterator, this function rereads the input in order to detect duplicates.

Otherwise, if OutputIt satisfies LegacyForwardIterator, and the value type of InputIt is the same as that of OutputIt, this function compare *d_first to *first.

Otherwise, this function compares *first to a local element copy.

For the overloads with an ExecutionPolicy, there may be a performance cost if the value type of ForwardIt1 is not both CopyConstructible and CopyAssignable.

Possible implementation

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

Example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>
 
int main()
{
    std::string s1 {"The      string    with many       spaces!"};
    std::cout << "before: " << s1 << '\n';
 
    std::string s2;
    std::unique_copy(s1.begin(), s1.end(), std::back_inserter(s2),
                     [](char c1, char c2) { return c1 == ' ' && c2 == ' '; });
 
    std::cout << "after:  " << s2 << '\n';
}

before: The      string    with many       spaces!
after:  The string with many spaces!

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also