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std::unique_copy

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< cpp‎ | algorithm
Revision as of 22:47, 31 May 2013 by P12bot (Talk | contribs)

 
 
 
Defined in header <algorithm>
template< class InputIt, class OutputIt >

ForwardIt unique_copy( InputIt first, InputIt last,

                       OutputIt d_first );
(1)
template< class InputIt, class OutputIt, class BinaryPredicate >

ForwardIt unique_copy( InputIt first, InputIt last,

                       OutputIt 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

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 ForwardIt can be dereferenced and then implicitly converted to both of them.

Type requirements
-
InputIt must meet the requirements of InputIterator.
-
OutputIt must meet the requirements of OutputIterator.
-
The type of dereferenced InputIt must meet the requirements of CopyAssignable.
-
The type of dereferenced InputIt must meet the requirements of CopyConstructible. if neither InputIt nor OutputIt satisfies ForwardIterator

Return value

Output iterator to the element past the last written element

Possible implementation

First version
template<class ForwardIt, class OutputIt>
ForwardIt unique_copy(ForwardIt first, ForwardIt last,
                      OutputIt d_first)
{
 
    if (first == last)
        return d_first;
 
    *d_first = *first;
     while (++first != last) {
        if (!(*d_first == *first)) {
            *(++d_first) = *first;
        }
    }
    return ++d_first;
}
Second version
template<class ForwardIt, class OutputIt, class BinaryPredicate>
ForwardIt unique_copy(ForwardIt first, ForwardIt last,
                            OutputIt d_first, BinaryPredicate p)
{
 
    if (first == last)
        return d_first;
 
    *d_first = *first;
    while (++first != last) {
        if (!p(*result, *first)) {
            *(++d_first) = *first;
        }
    }
    return ++d_first;
}

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!

Complexity

linear in the distance between first and last

See also

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