std::unique_copy

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

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

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

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

Copies elements from the source range [first, last) to the destination range beginning at d_first. For each group of consecutive equivalent elements, only the first element is copied.

If *d_first = *first is invalid(until C++20)*first is not writable to d_first(since C++20), the program is ill-formed.

If any of the following conditions is satisfied, the behavior is undefined:

• The source and destination ranges overlap.
• For the non-parallel overloads ((1,2)), given T as the value type of InputIt, all following conditions are satisfied:

• T is not CopyAssignable, or all following conditions are satisfied:

• T is not CopyConstructible.
• OutputIt does not the requirements of LegacyForwardIterator, or the value type of OutputIt is not T.

Parameters

Return value

The past-the-end iterator of the destination range.

Complexity

Given \(\scriptsize N\)N as std::distance(first, last):

Exceptions

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.

Possible implementation

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

Example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>

int main()
{
    std::string s1{"A string with mmmany letters!"};
    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 == 'm' && 'm' == c2; });
    
    std::cout << "After:  " << s2 << '\n';
}

Before: A string with mmmany letters!
After:  A string with many letters!

Defect reports

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

See also