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| <A HREF="fstream-h.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="functional-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>Function Objects</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>Objects with an <SAMP>operator()</SAMP> defined. They are used as arguments to templatized algorithms, in place of pointers to functions.</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <functional> |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <P>Function objects are objects with an <SAMP>operator()</SAMP> defined. They are important for the effective use of the standard library's generic algorithms, because the interface for each algorithmic template can accept either an object with an <SAMP>operator()</SAMP> defined, or a pointer to a function. The C++ Standard Library includes both a standard set of function objects, and a pair of classes that you can use as the base for creating your own function objects.</P> |
| <P>Function objects that take one argument are called <I>unary function objects</I>. Unary function objects must include the typedefs <SAMP>argument_type</SAMP> and <SAMP>result_type</SAMP>. Similarly, function objects that take two arguments are called <I>binary function objects</I> and, as such, must include the typedefs <SAMP>first_argument_type</SAMP>, <SAMP>second_argument_type</SAMP>, and <SAMP>result_type</SAMP>. </P> |
| <P>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> make the task of creating templatized function objects easier. The necessary typedefs for a unary or binary function object are included by inheriting from the appropriate function object class.</P> |
| <P>The function objects in the C++ Standard Library are listed below, together with a brief description of their operation. This Reference Guide also includes an alphabetic entry for each function.</P> |
| <H4><A NAME="Table 19">Table 19: C++ Standard Library function objects and their operations</A></H4> |
| <TABLE BORDER="1" CELLPADDING="3" CELLSPACING="3"> |
| <tr><td valign=top><B>Name </B> |
| </td> |
| <td valign=top><B>Operation</B> |
| </td> |
| </tr> |
| <tr><td valign=top colspan=2 rowspan=1><P CLASS="TABLE"><SAMP>arithmetic functions</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>plus</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>addition x + y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>minus</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>subtraction x - y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>multiplies</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>multiplication x * y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>divides</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>division x / y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>modulus</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>remainder x % y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>negate</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>negation - x</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top colspan=2 rowspan=1><P CLASS="TABLE"><SAMP>comparison functions</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>equal_to</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>equality test x == y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>not_equal_to</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>inequality test x != y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>greater</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>greater comparison x > y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>less</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>less-than comparison x < y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>greater_equal</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>greater than or equal comparison x >= y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>less_equal</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>less than or equal comparison x <= y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top colspan=2 rowspan=1><P CLASS="TABLE"><SAMP>logical functions</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>logical_and</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>logical conjunction x && y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>logical_or</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>logical disjunction x || y</SAMP></P> |
| </td> |
| </tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>logical_not</SAMP></P> |
| </td> |
| <td valign=top><P CLASS="TABLE"><SAMP>logical negation ! x</SAMP></P> |
| </td> |
| </tr> |
| </TABLE> |
| <A NAME="sec5"><H3>Interface</H3></A> |
| |
| <UL><PRE>namespace std { |
| |
| template <class Arg, class Result> |
| struct unary_function{ |
| typedef Arg argument_type; |
| typedef Result result_type; |
| }; |
| |
| template <class Arg1, class Arg2, class Result> |
| struct binary_function{ |
| typedef Arg1 first_argument_type; |
| typedef Arg2 second_argument_type; |
| typedef Result result_type; |
| }; |
| |
| // Arithmetic Operations |
| |
| template<class T> |
| struct plus : binary_function<T, T, T> { |
| T operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct minus : binary_function<T, T, T> { |
| T operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct multiplies : binary_function<T, T, T> { |
| T operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct divides : binary_function<T, T, T> { |
| T operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct modulus : binary_function<T, T, T> { |
| T operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct negate : unary_function<T, T> { |
| T operator() (const T&) const; |
| }; |
| |
| // Comparisons |
| |
| template <class T> |
| struct equal_to : binary_function<T, T, bool> { |
| bool operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct not_equal_to : binary_function<T, T, bool> { |
| bool operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct greater : binary_function<T, T, bool> { |
| bool operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct less : binary_function<T, T, bool> { |
| bool operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct greater_equal : binary_function<T, T, bool> { |
| bool operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct less_equal : binary_function<T, T, bool> { |
| bool operator() (const T&, const T&) const; |
| }; |
| |
| // Logical Comparisons |
| |
| template <class T> |
| struct logical_and : binary_function<T, T, bool> { |
| bool operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct logical_or : binary_function<T, T, bool> { |
| bool operator() (const T&, const T&) const; |
| }; |
| |
| template <class T> |
| struct logical_not : unary_function<T, T, bool> { |
| bool operator() (const T&, const T&) const; |
| }; |
| } |
| </PRE></UL> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // funct_ob.cpp |
| // |
| |
| #include <algorithm> |
| #include <deque> |
| #include <functional> |
| #include <iostream> |
| #include <vector> |
| |
| |
| // Create a new function object from unary_function. |
| template <class Arg, class Result> |
| struct factorial: public std::unary_function<Arg, Result> |
| { |
| Result operator() (const Arg &arg) { |
| Result a = 1; |
| for (Arg i = 2; i <= arg; i++) |
| a *= i; |
| return a; |
| } |
| }; |
| |
| |
| int main () |
| { |
| // Typedefs for convenience. |
| typedef std::deque<int, std::allocator<int> > deque; |
| typedef std::vector<long, std::allocator<long> > vector; |
| |
| // Initialize a deque with an array of integers. |
| deque::value_type arr[] = { 1, 2, 3, 4, 5, 6, 7 }; |
| deque d (arr, arr + sizeof arr / sizeof *arr); |
| |
| // Create an empty vector to store the factorials. |
| vector v; |
| |
| // Transform the numbers in the deque to their |
| // factorials and store in the vector. |
| std::transform(d.begin(), d.end(), |
| std::back_inserter(v), |
| factorial<deque::value_type, |
| vector::value_type>()); |
| |
| // Create an iterator to output deque elements. |
| std::ostream_iterator<deque::value_type, char, |
| std::char_traits<char> > outd(std::cout, " "); |
| |
| // Print the results. |
| std::cout << "The following numbers: \n "; |
| std::copy(d.begin(), d.end(), outd); |
| |
| // Create an iterator to output vector elements. |
| std::ostream_iterator<vector::value_type, char, |
| std::char_traits<char> > outv(std::cout, " "); |
| |
| std::cout << std::endl; |
| std::cout << "\nHave the factorials: \n "; |
| std::copy (v.begin(), v.end(), outv); |
| std::cout << std::endl; |
| |
| return 0; |
| } |
| |
| |
| Program Output: |
| </PRE></UL> |
| <UL><PRE>The following numbers: |
| 1 2 3 4 5 6 7 |
| |
| Have the factorials: |
| 1 2 6 24 120 720 5040 |
| </PRE></UL> |
| <A NAME="sec7"><H3>See Also</H3></A> |
| <P><B><I><A HREF="binary-function.html">binary_function</A></I></B>, <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</I></P> |
| |
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