first commit
This commit is contained in:
Jose Caban
124
extern/stdcxx/4.2.1/doc/stdlibug/33-2.html
vendored
Normal file
124
extern/stdcxx/4.2.1/doc/stdlibug/33-2.html
vendored
Normal file
@@ -0,0 +1,124 @@
|
||||
<!--
|
||||
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>Manipulators without Parameters</TITLE>
|
||||
<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
|
||||
<BODY BGCOLOR=#FFFFFF>
|
||||
<A HREF="33-1.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="33-3.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>33.2 Manipulators without Parameters</H2>
|
||||
<A NAME="idx802"><!></A>
|
||||
<P>Manipulators that do not have any parameters, like <SAMP>endl</SAMP>, are the simplest form of manipulator. The manipulator type <SAMP>manipT</SAMP> is a function pointer type, the manipulator <SAMP>Manip</SAMP> is the function pointer, and the associated function <SAMP>f</SAMP><SAMP><SUB>manipT</SUB></SAMP><SAMP>()</SAMP> is the function pointed to.</P>
|
||||
<A NAME="idx803"><!></A>
|
||||
<P>In iostreams, the following function pointer types serve as manipulators:</P>
|
||||
|
||||
<UL><PRE>
|
||||
(1) std::ios_base& (*)(std::ios_base&)
|
||||
(2) std::basic_ios<>& (*)(std::basic_ios<>&)
|
||||
(3) std::basic_istream<>& (*)(std::basic_istream<>&)
|
||||
(4) std::basic_ostream<>& (*)(std::basic_ostream<>&)
|
||||
</PRE></UL>
|
||||
<P>The signature of a manipulator function is not limited to the examples above. If you have created your own stream types, you will certainly want to use additional signatures as manipulators.</P>
|
||||
<A NAME="idx804"><!></A>
|
||||
<P>For the four manipulator types listed above, the stream classes already offer the required overloaded inserters and member functions. For input streams, extractors take the following form:</P>
|
||||
|
||||
<UL><PRE>
|
||||
template<class charT, class traits>
|
||||
std::basic_istream<charT, traits>&
|
||||
std::basic_istream<charT, traits>::operator>>
|
||||
(<I>input_stream_type</I>& (*pf)(<I>input_stream_type</I>&) )
|
||||
{ return (*pf)(*this); }
|
||||
</PRE></UL>
|
||||
<P>where the type of the argument <SAMP>pf</SAMP> is one of types (1) -- (3).</P>
|
||||
<A NAME="idx805"><!></A>
|
||||
<P>Similarly, for output streams we have:</P>
|
||||
|
||||
<UL><PRE>
|
||||
template<class charT, class traits>
|
||||
std::basic_ostream<charT, traits>&
|
||||
std::basic_ostream<charT, traits>::operator<<
|
||||
(<I>output_stream_type</I>& (*pf)(<I>output_stream_type</I>&))
|
||||
{ return (*pf)(*this); }
|
||||
</PRE></UL>
|
||||
<P>where the type of the argument <SAMP>pf</SAMP> is one of the types (1), (2), or (4).</P>
|
||||
<A NAME="3321"><H3>33.2.1 Examples of Manipulators without Parameters</H3></A>
|
||||
<A NAME="idx806"><!></A>
|
||||
<P>Let's look at the manipulator <SAMP>endl</SAMP> as an example of a manipulator without parameters. The manipulator <SAMP>endl</SAMP>, which can be applied solely to output streams, is a pointer to the following function of type (4):</P>
|
||||
|
||||
<UL><PRE>
|
||||
template<class charT, class traits>
|
||||
std::basic_ostream<charT, traits>&
|
||||
std::endl(std::basic_ostream<charT, traits>& os)
|
||||
{
|
||||
return os.put(os.widen('\n')).flush();
|
||||
}
|
||||
</PRE></UL>
|
||||
<P>Hence an expression like: </P>
|
||||
|
||||
<UL><PRE>
|
||||
std::cout << std::endl;
|
||||
</PRE></UL>
|
||||
<P>results in a call to the inserter:</P>
|
||||
|
||||
<UL><PRE>
|
||||
std::ostream& std::ostream::operator<<(std::ostream&
|
||||
(*pf)(std::ostream&))
|
||||
</PRE></UL>
|
||||
<P>with<SAMP> std::endl</SAMP> as the actual argument for <SAMP>pf</SAMP>. In other words, <SAMP>std::cout << std::endl;</SAMP> is equivalent to <SAMP>std::cout.operator<<(std::endl)</SAMP>. That is, inserting <SAMP>endl </SAMP>into a stream is really inserting the address of the template specialization <SAMP>std::endl<char, std::char_traits<char> ></SAMP> into the stream object <SAMP>std::cout</SAMP>. Inserting <SAMP>endl</SAMP> into the standard wide character stream object <SAMP>std::wcout</SAMP> inserts the address of the specialization of the same template on <SAMP>wchar_t</SAMP>, or <SAMP>std::endl<wchar_t, std::char_traits<wchar_t> ></SAMP>. Thanks to template argument deduction one need not bother to specify the actual template arguments.</P>
|
||||
<A NAME="idx807"><!></A>
|
||||
<P>Here is another manipulator, <SAMP>std::boolalpha</SAMP>, that can be applied to input <I>and</I> output streams. The manipulator <SAMP>boolalpha</SAMP> is a pointer to a function of type (1), since all it needs to access is the state encapsulated in the <SAMP>ios_base</SAMP> part of the stream object:</P>
|
||||
|
||||
<UL><PRE>
|
||||
std::ios_base& boolalpha(std::ios_base& strm)
|
||||
{
|
||||
strm.setf(std::ios_base::boolalpha);
|
||||
|
||||
return strm;
|
||||
}
|
||||
</PRE></UL>
|
||||
<A NAME="idx808"><!></A>
|
||||
<BLOCKQUOTE><HR><B>
|
||||
NOTE -- Every function that takes a reference to an <SAMP>ios_base</SAMP>, a <SAMP>basic_ios</SAMP>, a <SAMP>basic_ostream</SAMP>, or a <SAMP>basic_istream</SAMP>, and returns a reference to the same stream, can be used as a parameter-less manipulator.
|
||||
</B><HR></BLOCKQUOTE>
|
||||
<A NAME="3322"><H3>33.2.2 A Remark on the Manipulator endl</H3></A>
|
||||
<A NAME="idx809"><!></A>
|
||||
<P>The manipulator<SAMP> std::endl</SAMP> is often used for inserting the end-of-line character into a stream. However, <SAMP>endl</SAMP> does additionally flush the output stream, as you can see from the implementation of <SAMP>endl</SAMP> shown above. Flushing a stream, a relatively time-consuming operation that decreases performance, is unnecessary in most common situations. In the standard example:</P>
|
||||
|
||||
<UL><PRE>
|
||||
std::cout << "Hello world" << std::endl;
|
||||
</PRE></UL>
|
||||
<P>flushing is not necessary because the standard output stream <SAMP>cout</SAMP> is flushed automatically during program termination. Since no flush is required, the intent is probably to insert the end-of-line character. If you consider typing <SAMP>'\n'</SAMP> more trouble than typing <SAMP>endl</SAMP>, you can easily add a simple manipulator <SAMP>nl</SAMP> that inserts the end-of-line character, but refrains from flushing the stream.</P>
|
||||
|
||||
<BR>
|
||||
<HR>
|
||||
<A HREF="33-1.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="33-3.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>
|
||||
Reference in New Issue
Block a user