Standard Template Library Programmer's Guide

OutputIterator unique_copy(InputIterator first, InputIterator last, OutputIterator result);

template

OutputIterator unique_copy(InputIterator first, InputIterator last, OutputIterator result, BinaryPredicate binary_pred);

Unique_copy copies elements from the range [first, last) to a range beginning with result , except that in a consecutive group of duplicate elements only the first one is copied. The return value is the end of the range to which the elements are copied. This behavior is similar to the Unix filter uniq .

The reason there are two different versions of unique_copy is that there are two different definitions of what it means for a consecutive group of elements to be duplicates. In the first version, the test is simple equality: the elements in a range [f, l) are duplicates if, for every iterator i in the range, either i == f or else *i == *(i-1) . In the second, the test is an arbitrary Binary Predicate binary_pred : the elements in [f, l) are duplicates if, for every iterator i in the range, either i == f or else binary_pred(*i, *(i-1)) is true . [1]

Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.

For the first version:

• InputIterator is a model of Input Iterator.

• InputIterator 's value type is Equality Comparable.

• OutputIterator is a model of Output Iterator.

• InputIterator 's value type is convertible to a type in OutputIterator 's set of value types.

For the second version:

• InputIterator is a model of Input Iterator.

• BinaryPredicate is a model of Binary Predicate. [2]

• InputIterator 's value type is convertible to first argument type and to BinaryPredicate 's second argument type.

• OutputIterator is a model of Output Iterator.

• InputIterator 's value type is convertible to a type in OutputIterator 's set of value types.

• [first, last) is a valid range.

• There is enough space to hold all of the elements being copied. More formally, if there are n elements in the range [first, last) after duplicates are removed from consecutive groups, then [result, result + n) must be a valid range.

Linear. Exactly last – first applications of operator== (in the case of the first version of unique ) or of binary_pred (in the case of the second version), and at most last – first assignments.

Print all of the numbers in an array, but only print the first one in a consecutive group of identical numbers.

const int A[] = {2, 7, 7, 7, 1, 1, 8, 8, 8, 2, 8, 8};

unique_copy(A, A + sizeof(A) / sizeof(int), ostream_iterator(cout, " "));

// The output is "2 7 1 8 2 8".

[1] Strictly speaking, the first version of unique_copy is redundant: you can achieve the same functionality by using an object of class equal_to as the Binary Predicate argument. The first version is provided strictly for the sake of convenience: testing for equality is an important special case.

[2] BinaryPredicate is not required to be an equivalence relation. You should be cautious, though, about using unique_copy with a Binary Predicate that is not an equivalence relation: you could easily get unexpected results.

Binary Predicate, unique , remove_copy , remove_copy_if , adjacent_find

Category: algorithms

Component type: function

template

void reverse(BidirectionalIterator first, BidirectionalIterator last);

Reverse reverses a range. That is: for every i such that 0 <= i <= (last – first) / 2) , it exchanges *(first + i) and *(last – (i + 1)) .

Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.

• BidirectionalIterator is a model of Bidirectional Iterator.

• BidirectionalIterator is mutable.

• [first, last) is a valid range.

Linear: reverse(first, last) makes (last – first) / 2 calls to swap .

vector V;

V.push_back(0);

V.push_back(1);

V.push_back(2);

copy(V.begin(), V.end(), ostream_iterator(cout, " "));

// Output: 0 1 2

reverse(V.begin(), V.end());

copy(V.begin(), V.end(), ostream_iterator(cout, " "));

// Output: 2 1 0

reverse_copy

Category: algorithms

Component type: function

template

OutputIterator reverse_copy(BidirectionalIterator first, BidirectionalIterator last, OutputIterator result);

Reverse_copy copies elements from the range [first, last) to the range [result, result + (last – first)) such that the copy is a reverse of the original range. Specifically: for every i such that 0 <= i < (last – first) , reverse_copy performs the assignment *(result + (last – first) – i) = *(first + i) .

The return value is result + (last – first) .

Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.

• BidirectionalIterator is a model of Bidirectional Iterator.

• OutputIterator is a model of Output Iterator.

• The value type of BidirectionalIterator is convertible to a type in OutputIterator's set of value types.

• [first, last) is a valid range.

• There is enough space to hold all of the elements being copied. More formally, the requirement is that [result, result + (last – first)) is a valid range.

• The ranges [first, last) and [result, result + (last – first)) do not overlap.

Linear: exactly last – first assignments.

vector V;