• The ordering on objects of InputIterator1's value type is a strict weak ordering, as defined in the LessThan Comparable requirements.
For the second version:
• InputIterator1 is a model of Input Iterator.
• InputIterator2 is a model of Input Iterator.
• InputIterator1 and InputIterator2 have the same value type.
• StrictWeakOrdering is a model of Strict Weak Ordering.
• 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 LessThan Comparable 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
