std::unique_copy

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Defined in header <algorithm>

template< class ForwardIterator, class OutputIterator >

ForwardIterator unique_copy( ForwardIterator first, ForwardIterator last,

                             OutputIterator d_first );
(1)
template< class ForwardIterator, class OutputIterator, class BinaryPredicate >

ForwardIterator unique_copy( ForwardIterator first, ForwardIterator last,

                             OutputIterator d_first, BinaryPredicate p );
(2)

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. The first version uses operator== to compare the elements, the second version uses the given binary predicate p.

Contents

[edit] Parameters

first, last - the range of elements to process
d_first - the beginning of the destination range
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);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type ForwardIterator can be dereferenced and then implicitly converted to both of them.

[edit] Return value

output iterator to the element past the last written element

[edit] Equivalent function

[edit] Example

The following program trims all multiple consecutive spaces in a const string and prints the result

#include <string>
#include <iostream>
#include <algorithm>
#include <iterator>
 
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';
}

Output:

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

[edit] Complexity

linear in the distance between first and last

[edit] See also

adjacent_find
finds two identical (or some other relationship) items adjacent to each other
(function template)
unique
removes consecutive duplicate elements in a range
(function template)