Category: algorithms | Component type: function |
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);
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 function object comp.
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
[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.