| <!-- |
| Licensed to the Apache Software Foundation (ASF) under one or more |
| contributor license agreements. See the NOTICE file distributed |
| with this work for additional information regarding copyright |
| ownership. The ASF licenses this file to you under the Apache |
| License, Version 2.0 (the License); you may not use this file |
| except in compliance with the License. You may obtain a copy of |
| the License at |
| |
| http://www.apache.org/licenses/LICENSE-2.0 |
| |
| Unless required by applicable law or agreed to in writing, software |
| distributed under the License is distributed on an "AS IS" BASIS, |
| WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or |
| implied. See the License for the specific language governing |
| permissions and limitations under the License. |
| |
| Copyright 1999-2007 Rogue Wave Software, Inc. |
| --> |
| |
| <HTML> |
| <HEAD> |
| <TITLE>Functions</TITLE> |
| <LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD> |
| <BODY BGCOLOR=#FFFFFF> |
| <A HREF="3.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="3-2.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library User's Guide</B></DIV> |
| <H2>3.1 Functions</H2> |
| <A NAME="idx43"><!></A> |
| <P>A number of algorithms provided in the C++ Standard Library accept functions as arguments. A simple example is the algorithm <SAMP>std::for_each()</SAMP>, which invokes a function, passed as an argument, on each value held in a container. For example, the following code fragment applies the <SAMP>printElement()</SAMP> function to produce output describing each element in a list of integer values:</P> |
| |
| <UL><PRE> |
| void printElement(int value) |
| { |
| std::cout << "The list contains " << value << std::endl; |
| } |
| |
| int main() |
| { |
| std::list<int> aList; |
| ... |
| std::for_each(aList.begin(), aList.end(), printElement); |
| } |
| </PRE></UL> |
| <P><I>Binary functions</I> take two arguments, and are often applied to values from two different sequences. For example, suppose we have a list of strings and a list of integers. For each element in the first list we wish to replicate the string the number of times given by the corresponding value in the second list. We can perform this easily using the function <SAMP>std::transform()</SAMP> from the C++ Standard Library. First, we define a binary function with the desired characteristics:</P> |
| |
| <UL><PRE> |
| std::string stringRepeat(const std::string& base, int number) |
| // replicate base the given number of times |
| { |
| std::string result; // initially the result is empty |
| while (number--) result += base; |
| return result; |
| } |
| </PRE></UL> |
| <P>The following call on <SAMP>std::transform()</SAMP> then produces the desired effect:</P> |
| |
| <UL><PRE> |
| std::list<string> words; |
| std::list<int> counts; |
| ... |
| std::transform(words.begin(), words.end(), |
| counts.begin(), words.begin(), stringRepeat); |
| </PRE></UL> |
| <P>Transforming the strings <SAMP>"one"</SAMP>, <SAMP>"two"</SAMP>, <SAMP>"three"</SAMP> with the values <SAMP>3</SAMP>, <SAMP>2</SAMP>, <SAMP>3</SAMP> would yield the result <SAMP>"oneoneone"</SAMP>, <SAMP>"twotwo"</SAMP>, <SAMP>"threethreethree"</SAMP>.</P> |
| |
| <BR> |
| <HR> |
| <A HREF="3.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="3-2.html"><IMG SRC="images/bnext.gif" WIDTH=20 HEIGHT=21 ALT="Next file" BORDER=O></A> |
| |
| <!-- Google Analytics tracking code --> |
| <script src="http://www.google-analytics.com/urchin.js" type="text/javascript"> |
| </script> |
| <script type="text/javascript"> |
| _uacct = "UA-1775151-1"; |
| urchinTracker(); |
| </script> |
| <!-- end of Google Analytics tracking code --> |
| |
| </BODY> |
| </HTML> |
