std::unique_copy

Header: <algorithm>

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.

# Declarations

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

(constexpr since C++20)

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

(since C++17)

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

(constexpr since C++20)

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

(since C++17)

# Parameters

• first, last: the range of elements to process
• d_first: the beginning of the destination range
• policy: the execution policy to use
• p: binary predicate which returns true if the elements should be treated as equal. The signature of the predicate function should be equivalent to the following: bool pred(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 InputIt can be dereferenced and then implicitly converted to both of them.

# Return value

Output iterator to the element past the last written element.

# 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.

# 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';
}

# Defect reports

# See also

• adjacent_find
• unique
• copycopy_if
• ranges::unique_copy