includes

Category: algorithms		Component type: function

Prototype

Includes is an overloaded name; there are actually two includes functions.

template <class InputIterator1, class InputIterator2>
bool includes(InputIterator1 first1, InputIterator1 last1,
              InputIterator2 first2, InputIterator2 last2);

template <class InputIterator1, class InputIterator2, class StrictWeakOrdering>
bool includes(InputIterator1 first1, InputIterator1 last1,
              InputIterator2 first2, InputIterator2 last2, 
              StrictWeakOrdering comp);

Description

Includes tests whether one sorted range includes another sorted range. That is, it returns true if and only if, for every element in [first2, last2), an equivalent element [1] is also present in [first1, last1) [2]. Both [first1, last1) and [first2, last2) must be sorted in ascending order.

The two versions of includes differ in how they define whether one element is less than another. The first version compares objects using operator<, and the second compares objects using the functors comp.

Definition

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

Requirements on types

For the first version:

• InputIterator1 is a model of InputIterator.
• InputIterator2 is a model of InputIterator.
• InputIterator1 and InputIterator2 have the same value type.
• InputIterator's value type is a model of LessThanComparable.
• The ordering on objects of InputIterator1's value type is a strict weak ordering, as defined in the LessThanComparable requirements.

For the second version:

• InputIterator1 is a model of InputIterator.
• InputIterator2 is a model of InputIterator.
• InputIterator1 and InputIterator2 have the same value type.
• StrictWeakOrdering is a model of StrictWeakOrdering.
• InputIterator1's value type is convertible to StrictWeakOrdering's argument type.

Preconditions

For the first version:

• [first1, last1) is a valid range.
• [first2, last2) is a valid range.
• [first1, last1) is ordered in ascending order according to operator<. That is, for every pair of iterators i and j in [first1, last1) such that i precedes j, *j < *i is false.
• [first2, last2) is ordered in ascending order according to operator<. That is, for every pair of iterators i and j in [first2, last2) such that i precedes j, *j < *i is false.

For the second version:

• [first1, last1) is a valid range.
• [first2, last2) is a valid range.
• [first1, last1) is ordered in ascending order according to comp. That is, for every pair of iterators i and j in [first1, last1) such that i precedes j, comp(*j, *i) is false.
• [first2, last2) is ordered in ascending order according to comp. That is, for every pair of iterators i and j in [first2, last2) such that i precedes j, comp(*j, *i) is false.

Complexity

Linear. Zero comparisons if either [first1, last1) or [first2, last2) is an empty range, otherwise at most 2 * ((last1 - first1) + (last2 - first2)) - 1 comparisons.

Example

int A1[] = { 1, 2, 3, 4, 5, 6, 7 };
int A2[] = { 1, 4, 7 };
int A3[] = { 2, 7, 9 };
int A4[] = { 1, 1, 2, 3, 5, 8, 13, 21 };
int A5[] = { 1, 2, 13, 13 };
int A6[] = { 1, 1, 3, 21 };

const int N1 = sizeof(A1) / sizeof(int);
const int N2 = sizeof(A2) / sizeof(int);
const int N3 = sizeof(A3) / sizeof(int);
const int N4 = sizeof(A4) / sizeof(int);
const int N5 = sizeof(A5) / sizeof(int);
const int N6 = sizeof(A6) / sizeof(int);

cout << "A2 contained in A1: " 
     << (includes(A1, A1 + N1, A2, A2 + N2) ? "true" : "false") << endl;
cout << "A3 contained in A1: " 
     << (includes(A1, A1 + N2, A3, A3 + N3) ? "true" : "false") << endl;
cout << "A5 contained in A4: " 
     << (includes(A4, A4 + N4, A5, A5 + N5) ? "true" : "false") << endl;
cout << "A6 contained in A4: " 
     << (includes(A4, A4 + N4, A6, A6 + N6) ? "true" : "false") << endl;

The output is:

A2 contained in A1: true
A3 contained in A1: false
A5 contained in A4: false
A6 contained in A4: true

Notes

[1] This reads "an equivalent element" rather than "the same element" because the ordering by which the input ranges are sorted is permitted to be a strict weak ordering that is not a total ordering: there might be values x and y that are equivalent (that is, neither x < y nor y < x is true) but not equal. See the LessThanComparable requirements for a fuller discussion.) If you're using a total ordering (if you're using strcmp, for example, or if you're using ordinary arithmetic comparison on integers), then you can ignore this technical distinction: for a total ordering, equality and equivalence are the same.

[2] Note that the range [first2, last2) may contain a consecutive range of equivalent elements: there is no requirement that every element in the range be unique. In this case, includes will return false unless, for every element in [first2, last2), a distinct equivalent element is also present in [first1, last1). That is, if a certain value appears n times in [first2, last2) and m times in [first1, last1), then includes will return false if m < n.

See also

set_union, set_intersection, set_difference, set_symmetric_difference, sort