Difference of A3 and A4: B B g H
Notes [1] Even this is not a completely precise description, 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) but not equal. See the LessThan Comparable requirements for a fuller discussion. The output range consists of those elements from [first1, last1) for which equivalent elements do not exist in [first2, last2). Specifically, if the range [first1, last1) contains m elements that are equivalent to each other and the range [first2, last2) contains n elements from that equivalence class (where either m or n may be zero), then the output range contains the lastmax(m – n, 0) of these elements from [first1, last1). Note that this precision is only important if elements can be equivalent but not equal. 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.
See also includes, set_union, set_intersection, set_symmetric_difference, sort
Category: algorithms
Component type: function
Prototype Set_symmetric_difference is an overloaded name; there are actually two set_symmetric_difference functions.
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_symmetric_difference(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result);
template <class InputIterator1, class InputIterator2, class OutputIterator, class StrictWeakOrdering>
OutputIterator set_symmetric_difference(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result, StrictWeakOrdering comp);
Description Set_symmetric_difference constructs a sorted range that is the set symmetric difference of the sorted ranges [first1, last1) and [first2, last2) . The return value is the end of the output range.
In the simplest case, set_symmetric_difference performs a set theoretic calculation: it constructs the union of the two sets A – B and B – A, where A and B are the two input ranges. That is, the output range contains a copy of every element that is contained in [first1, last1) but not [first2, last2), and a copy of every element that is contained in [first2, last2) but not [first1, last1). The general case is more complicated, because the input ranges may contain duplicate elements. The generalization is that if a value appears m times in [first1, last1) and n times in [first2, last2) (where m or n may be zero), then it appears |m-n| times in the output range. [1] Set_symmetric_difference is stable, meaning that the relative order of elements within each input range is preserved.
The two versions of set_symmetric_difference 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 a function object 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 Input Iterator.
• InputIterator2 is a model of Input Iterator.
• OutputIterator is a model of Output Iterator.
• InputIterator1 and InputIterator2 have the same value type.
• InputIterator's value type is a model of LessThan Comparable.
• The ordering on objects of InputIterator1's value type is a strict weak ordering, as defined in the LessThan Comparable requirements.
• InputIterator's value type is convertible to a type in OutputIterator's set of value types.
For the second version:
• InputIterator1 is a model of Input Iterator.
• InputIterator2 is a model of Input Iterator.
• OutputIterator is a model of Output Iterator.
• StrictWeakOrdering is a model of Strict Weak Ordering.
• InputIterator1 and InputIterator2 have the same value type.
• InputIterator1's value type is convertible to StrictWeakOrdering's argument type.
• InputIterator's value type is convertible to a type in OutputIterator's set of value types.
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.
• There is enough space to hold all of the elements being copied. More formally, the requirement is that [result, result + n) is a valid range, where n is the number of elements in the union of the two input ranges.
• [first1, last1) and [result, result + n) do not overlap.
