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<H1>set_symmetric_difference</H1>
<Table CellPadding=0 CellSpacing=0 width=100%>
<TR>
<TD Align=left><Img src = "algorithms.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD>
<TD Align=right><Img src = "function.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD>
</TR>
<TR>
<TD Align=left VAlign=top><b>Category</b>: algorithms</TD>
<TD Align=right VAlign=top><b>Component type</b>: function</TD>
</TR>
</Table>
<h3>Prototype</h3>
<tt>Set_symmetric_difference</tt> is an overloaded name; there are actually two
<tt>set_symmetric_difference</tt> functions.
<pre>
template <class <A href="InputIterator.html">InputIterator</A>1, class <A href="InputIterator.html" tppabs="http://www.sgi.com/Technology/STL/InputIterator.shtml">InputIterator</A>2, class <A href="OutputIterator.html" tppabs="http://www.sgi.com/Technology/STL/OutputIterator.shtml">OutputIterator</A>>
OutputIterator set_symmetric_difference(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2,
InputIterator2 last2,
OutputIterator result);
template <class <A href="InputIterator.html">InputIterator</A>1, class <A href="InputIterator.html" tppabs="http://www.sgi.com/Technology/STL/InputIterator.shtml">InputIterator</A>2, class <A href="OutputIterator.html" tppabs="http://www.sgi.com/Technology/STL/OutputIterator.shtml">OutputIterator</A>,
class <A href="StrictWeakOrdering.html">StrictWeakOrdering</A>>
OutputIterator set_symmetric_difference(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2,
InputIterator2 last2,
OutputIterator result,
StrictWeakOrdering comp);
</pre>
<h3>Description</h3>
<tt>Set_symmetric_difference</tt> constructs a sorted range that is the set symmetric
difference of the sorted ranges <tt>[first1, last1)</tt> and <tt>[first2,
last2)</tt>. The return value is the end of the output range.
<P>
In the simplest case, <tt>set_symmetric_difference</tt> performs a set
theoretic calculation: it constructs the union of the two sets <tt>A - B</tt>
and <tt>B - A</tt>, where <tt>A</tt> and <tt>B</tt> are the two input ranges. That is, the
output range contains a copy of every element that is contained in
<tt>[first1, last1)</tt> but not <tt>[first2, last2)</tt>, and a copy of every element
that is contained in <tt>[first2, last2)</tt> but not <tt>[first1, last1)</tt>.
The general case is more complicated, because the input ranges may
contain duplicate elements. The generalization is that if a value
appears <tt>m</tt> times in <tt>[first1, last1)</tt> and <tt>n</tt> times in <tt>[first2,
last2)</tt> (where <tt>m</tt> or <tt>n</tt> may be zero), then it appears <tt>|m-n|</tt>
times in the output range. <A href="#1">[1]</A> <tt>Set_symmetric_difference</tt> is stable,
meaning that the relative order of elements within each input range
is preserved.
<P>
The two versions of <tt>set_symmetric_difference</tt> differ in how they
define whether one element is less than another. The first version
compares objects using <tt>operator<</tt>, and the second compares
objects using a <A href="functors.html">function object</A> <tt>comp</tt>.
<h3>Definition</h3>
Defined in <A href="algo.h">algo.h</A>.
<h3>Requirements on types</h3>
For the first version:
<UL>
<LI>
<tt>InputIterator1</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.
<LI>
<tt>InputIterator2</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.
<LI>
<tt>OutputIterator</tt> is a model of <A href="OutputIterator.html">Output Iterator</A>.
<LI>
<tt>InputIterator1</tt> and <tt>InputIterator2</tt> have the same value type.
<LI>
<tt>InputIterator</tt>'s value type is a model of <A href="LessThanComparable.html">LessThan Comparable</A>.
<LI>
The ordering on objects of <tt>InputIterator1</tt>'s value type is a <i>strict
weak ordering</i>, as defined in the <A href="LessThanComparable.html">LessThan Comparable</A> requirements.
<LI>
<tt>InputIterator</tt>'s value type is convertible to a type in
<tt>OutputIterator</tt>'s set of value types.
</UL>
For the second version:
<UL>
<LI>
<tt>InputIterator1</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.
<LI>
<tt>InputIterator2</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.
<LI>
<tt>OutputIterator</tt> is a model of <A href="OutputIterator.html">Output Iterator</A>.
<LI>
<tt>StrictWeakOrdering</tt> is a model of <A href="StrictWeakOrdering.html">Strict Weak Ordering</A>.
<LI>
<tt>InputIterator1</tt> and <tt>InputIterator2</tt> have the same value type.
<LI>
<tt>InputIterator1</tt>'s value type is convertible to <tt>StrictWeakOrdering</tt>'s
argument type.
<LI>
<tt>InputIterator</tt>'s value type is convertible to a type in
<tt>OutputIterator</tt>'s set of value types.
</UL>
<h3>Preconditions</h3>
For the first version:
<UL>
<LI>
<tt>[first1, last1)</tt> is a valid range.
<LI>
<tt>[first2, last2)</tt> is a valid range.
<LI>
<tt>[first1, last1)</tt> is ordered in ascending order according to
<tt>operator<</tt>. That is, for every pair of iterators <tt>i</tt> and <tt>j</tt>
in <tt>[first1, last1)</tt> such that <tt>i</tt> precedes <tt>j</tt>,
<tt>*j < *i</tt> is <tt>false</tt>.
<LI>
<tt>[first2, last2)</tt> is ordered in ascending order according to
<tt>operator<</tt>. That is, for every pair of iterators <tt>i</tt> and <tt>j</tt>
in <tt>[first2, last2)</tt> such that <tt>i</tt> precedes <tt>j</tt>,
<tt>*j < *i</tt> is <tt>false</tt>.
<LI>
There is enough space to hold all of the elements being copied.
More formally, the requirement is that
<tt>[result, result + n)</tt> is a valid range, where <tt>n</tt> is the number
of elements in the symmetric difference of the two input ranges.
<LI>
<tt>[first1, last1)</tt> and <tt>[result, result + n)</tt> do not overlap.
<LI>
<tt>[first2, last2)</tt> and <tt>[result, result + n)</tt> do not overlap.
</UL>
For the second version:
<UL>
<LI>
<tt>[first1, last1)</tt> is a valid range.
<LI>
<tt>[first2, last2)</tt> is a valid range.
<LI>
<tt>[first1, last1)</tt> is ordered in ascending order according to
<tt>comp</tt>. That is, for every pair of iterators <tt>i</tt> and <tt>j</tt>
in <tt>[first1, last1)</tt> such that <tt>i</tt> precedes <tt>j</tt>,
<tt>comp(*j, *i)</tt> is <tt>false</tt>.
<LI>
<tt>[first2, last2)</tt> is ordered in ascending order according to
<tt>comp</tt>. That is, for every pair of iterators <tt>i</tt> and <tt>j</tt>
in <tt>[first2, last2)</tt> such that <tt>i</tt> precedes <tt>j</tt>,
<tt>comp(*j, *i)</tt> is <tt>false</tt>.
<LI>
There is enough space to hold all of the elements being copied.
More formally, the requirement is that
<tt>[result, result + n)</tt> is a valid range, where <tt>n</tt> is the number
of elements in the symmetric difference of the two input ranges.
<LI>
<tt>[first1, last1)</tt> and <tt>[result, result + n)</tt> do not overlap.
<LI>
<tt>[first2, last2)</tt> and <tt>[result, result + n)</tt> do not overlap.
</UL>
<h3>Complexity</h3>
Linear. Zero comparisons if either <tt>[first1, last1)</tt> or <tt>[first2, last2)</tt>
is empty, otherwise at most <tt>2 * ((last1 - first1) + (last2 - first2))
- 1</tt> comparisons.
<h3>Example</h3>
<pre>
inline bool lt_nocase(char c1, char c2) { return tolower(c1) < tolower(c2); }
int main()
{
int A1[] = {1, 3, 5, 7, 9, 11};
int A2[] = {1, 1, 2, 3, 5, 8, 13};
char A3[] = {'a', 'b', 'b', 'B', 'B', 'f', 'g', 'h', 'H'};
char A4[] = {'A', 'B', 'B', 'C', 'D', 'F', 'F', 'H' };
const int N1 = sizeof(A1) / sizeof(int);
const int N2 = sizeof(A2) / sizeof(int);
const int N3 = sizeof(A3);
const int N4 = sizeof(A4);
cout << "Symmetric difference of A1 and A2: ";
set_symmetric_difference(A1, A1 + N1, A2, A2 + N2,
ostream_iterator<int>(cout, " "));
cout << endl
<< "Symmetric difference of A3 and A4: ";
set_symmetric_difference(A3, A3 + N3, A4, A4 + N4,
ostream_iterator<char>(cout, " "),
lt_nocase);
cout << endl;
}
</pre>
<P>
The output is
<pre>
Symmetric difference of A1 and A2: 1 2 7 8 9 11 13
Symmetric difference of A3 and A4: B B C D F g H
</pre>
<h3>Notes</h3>
<P><A name="1">[1]</A>
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 <tt>x</tt> and <tt>y</tt> that are equivalent (that is, neither <tt>x < y</tt> nor
<tt>y < x</tt>) but not equal. See the <A href="LessThanComparable.html">LessThan Comparable</A>
requirements for a more complete discussion. The output range consists of
those elements from <tt>[first1, last1)</tt> for which equivalent elements do
not exist in <tt>[first2, last2)</tt>, and
those elements from <tt>[first2, last2)</tt> for which equivalent elements do
not exist in <tt>[first1, last1)</tt>.
Specifically, suppose that the range
<tt>[first1, last1)</tt> contains <tt>m</tt> elements that are equivalent to each
other and the range <tt>[first2, last2)</tt> contains <tt>n</tt> elements from that
equivalence class (where either <tt>m</tt> or <tt>n</tt> may be zero). If <tt>m > n</tt>
then the output range contains the <i>last</i> <tt>m - n</tt> of these
elements elements from <tt>[first1, last1)</tt>, and if <tt>m < n</tt> then the
output range contains the last <tt>n - m</tt> of these elements elements
from <tt>[first2, last2)</tt>.
<h3>See also</h3>
<tt><A href="includes.html">includes</A></tt>, <tt><A href="set_union.html" tppabs="http://www.sgi.com/Technology/STL/set_union.shtml">set_union</A></tt>, <tt><A href="set_intersection.html" tppabs="http://www.sgi.com/Technology/STL/set_intersection.shtml">set_intersection</A></tt>,
<tt><A href="set_difference.html">set_difference</A></tt>, <tt><A href="sort.html" tppabs="http://www.sgi.com/Technology/STL/sort.shtml">sort</A></tt>
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