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| <HTML> |
| <HEAD> |
| <TITLE>Negators</TITLE> |
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| <A HREF="negate.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="new-h.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library Reference Guide</B></DIV> |
| <H2>Negators</H2> |
| <P><B>Library:</B> <A HREF="2-4.html">General utilities</A></P><UL> |
| <LI><A HREF="#sec1">Local Index</A></LI> |
| <LI><A HREF="#sec2">Summary</A></LI> |
| <LI><A HREF="#sec3">Synopsis</A></LI> |
| <LI><A HREF="#sec4">Description</A></LI> |
| <LI><A HREF="#sec5">Interface</A></LI> |
| <LI><A HREF="#sec6">Example</A></LI> |
| <LI><A HREF="#sec7">See Also</A></LI> |
| <LI><A HREF="#sec8">Standards Conformance</A></LI> |
| </UL> |
| <A NAME="sec1"><H3>Local Index</H3></A> |
| No Entries |
| <A NAME="sec2"><H3>Summary</H3></A> |
| <P>Function adaptors and function objects used to reverse the sense of predicate function objects</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <functional> |
| |
| namespace std { |
| template <class Predicate> |
| class unary_negate; |
| |
| template <class Predicate> |
| unary_negate<Predicate> not1(const Predicate&); |
| |
| template <class Predicate> |
| class binary_negate; |
| |
| template <class Predicate> |
| binary_negate<Predicate> not2(const Predicate&); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <P>Negators <SAMP><A HREF="not1.html">not1()</A></SAMP> and <SAMP><A HREF="not2.html">not2()</A></SAMP> are functions that take predicate function objects as arguments and return predicate function objects with the opposite sense. Negators work only with function objects defined as subclasses of the classes <B><I><A HREF="unary-function.html">unary_function</A></I></B> and <B><I><A HREF="binary-function.html">binary_function</A></I></B>. <SAMP>not1()</SAMP> accepts and returns unary predicate function objects. <SAMP>not2()</SAMP> accepts and returns binary predicate function objects.</P> |
| <P><B><I><A HREF="unary-negate.html">unary_negate</A></I></B> and <B><I><A HREF="binary-negate.html">binary_negate</A></I></B> are function object classes that include return types for the negators, <SAMP><A HREF="not1.html">not1()</A></SAMP> and <SAMP><A HREF="not2.html">not2()</A></SAMP>.</P> |
| <A NAME="sec5"><H3>Interface</H3></A> |
| |
| <UL><PRE>namespace std { |
| |
| template <class Predicate> |
| class unary_negate |
| : public unary_function |
| <typename Predicate::argument_type, bool> { |
| |
| public: |
| explicit unary_negate (const Predicate&); |
| bool operator() (const argument_type&) const; |
| }; |
| |
| template<class Predicate> |
| unary_negate <Predicate> not1(const Predicate&); |
| } |
| template<class Predicate> |
| class binary_negate |
| : public binary_function |
| <typename Predicate::first_argument_type, |
| typename Predicate::second_argument_type, bool> |
| { |
| public: |
| explicit binary_negate (const Predicate&); |
| bool operator() (const first_argument_type&, |
| const second_argument_type&) const; |
| }; |
| |
| template <class Predicate> |
| binary_negate<Predicate> not2 (const Predicate&); |
| </PRE></UL> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // negator.cpp |
| // |
| |
| #include <functional> // for unary_function |
| #include <iostream> // for boolalpha, cout, endl |
| |
| |
| // Create a new predicate from unary_function. |
| template <class Arg> |
| struct is_odd : public std::unary_function<Arg, bool> |
| { |
| bool operator() (const Arg &arg1) const { |
| return arg1 % 2 != 0; |
| } |
| }; |
| |
| |
| int main () |
| { |
| std::less<int> less_func; |
| |
| // Use not2 on less. |
| std::cout << std::boolalpha |
| << less_func (1, 4) << '\n' |
| << less_func (4, 1) << '\n' |
| << std::not2 (std::less<int>())(1, 4) << '\n' |
| << std::not2 (std::less<int>())(4, 1) << '\n'; |
| |
| // Create an instance of our predicate. |
| is_odd<int> odd; |
| |
| // Use not1 on our user defined predicate. |
| std::cout << odd (1) << '\n' |
| << odd (4) << '\n' |
| << std::not1 (odd)(1) << '\n' |
| << std::not1 (odd)(4) << std::endl; |
| |
| return 0; |
| } |
| |
| |
| Program Output: |
| </PRE></UL> |
| <UL><PRE>true |
| false |
| false |
| true |
| true |
| false |
| false |
| true |
| </PRE></UL> |
| <A NAME="sec7"><H3>See Also</H3></A> |
| <P><A HREF="algorithms.html">Algorithms</A>, <B><I><A HREF="binary-function.html">binary_function</A></I></B>, <A HREF="functionobjects.html">Function Objects</A>, <B><I><A HREF="unary-function.html">unary_function</A></I></B></P> |
| <A NAME="sec8"><H3>Standards Conformance</H3></A> |
| <P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 20.3.5</I></P> |
| |
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