gcc/libstdc++-v3/doc/html/manual/io_and_c.html

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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Interacting with C</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.75.2"/><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="io.html" title="Chapter 13.  Input and Output"/><link rel="prev" href="fstreams.html" title="File Based Streams"/><link rel="next" href="atomics.html" title="Chapter 14.  Atomics"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Interacting with C</th></tr><tr><td align="left"><a accesskey="p" href="fstreams.html">Prev</a> </td><th width="60%" align="center">Chapter 13. 
  Input and Output
  
</th><td align="right"> <a accesskey="n" href="atomics.html">Next</a></td></tr></table><hr/></div><div class="section" title="Interacting with C"><div class="titlepage"><div><div><h2 class="title"><a id="std.io.c"/>Interacting with C</h2></div></div></div><div class="section" title="Using FILE* and file descriptors"><div class="titlepage"><div><div><h3 class="title"><a id="std.io.c.FILE"/>Using FILE* and file descriptors</h3></div></div></div><p>
      See the <a class="link" href="ext_io.html" title="Chapter 26. Input and Output">extensions</a> for using
      <span class="type">FILE</span> and <span class="type">file descriptors</span> with
      <code class="classname">ofstream</code> and
      <code class="classname">ifstream</code>.
    </p></div><div class="section" title="Performance"><div class="titlepage"><div><div><h3 class="title"><a id="std.io.c.sync"/>Performance</h3></div></div></div><p>
      Pathetic Performance? Ditch C.
    </p><p>It sounds like a flame on C, but it isn't.  Really.  Calm down.
      I'm just saying it to get your attention.
   </p><p>Because the C++ library includes the C library, both C-style and
      C++-style I/O have to work at the same time.  For example:
   </p><pre class="programlisting">
     #include &lt;iostream&gt;
     #include &lt;cstdio&gt;

     std::cout &lt;&lt; "Hel";
     std::printf ("lo, worl");
     std::cout &lt;&lt; "d!\n";
   </pre><p>This must do what you think it does.
   </p><p>Alert members of the audience will immediately notice that buffering
      is going to make a hash of the output unless special steps are taken.
   </p><p>The special steps taken by libstdc++, at least for version 3.0,
      involve doing very little buffering for the standard streams, leaving
      most of the buffering to the underlying C library.  (This kind of
      thing is tricky to get right.)
      The upside is that correctness is ensured.  The downside is that
      writing through <code class="code">cout</code> can quite easily lead to awful
      performance when the C++ I/O library is layered on top of the C I/O
      library (as it is for 3.0 by default).  Some patches have been applied
      which improve the situation for 3.1.
   </p><p>However, the C and C++ standard streams only need to be kept in sync
      when both libraries' facilities are in use.  If your program only uses
      C++ I/O, then there's no need to sync with the C streams.  The right
      thing to do in this case is to call
   </p><pre class="programlisting">
     #include <span class="emphasis"><em>any of the I/O headers such as ios, iostream, etc</em></span>

     std::ios::sync_with_stdio(false);
   </pre><p>You must do this before performing any I/O via the C++ stream objects.
      Once you call this, the C++ streams will operate independently of the
      (unused) C streams.  For GCC 3.x, this means that <code class="code">cout</code> and
      company will become fully buffered on their own.
   </p><p>Note, by the way, that the synchronization requirement only applies to
      the standard streams (<code class="code">cin</code>, <code class="code">cout</code>,
      <code class="code">cerr</code>,
      <code class="code">clog</code>, and their wide-character counterchapters).  File stream
      objects that you declare yourself have no such requirement and are fully
      buffered.
   </p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="fstreams.html">Prev</a> </td><td align="center"><a accesskey="u" href="io.html">Up</a></td><td align="right"> <a accesskey="n" href="atomics.html">Next</a></td></tr><tr><td align="left" valign="top">File Based Streams </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Chapter 14. 
  Atomics
  
</td></tr></table></div></body></html>
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2009-04-15  Benjamin Kosnik  <bkoz@redhat.com>

	* doc/html: Regenerate.

From-SVN: r146140

											
										
										
											2009-04-16 01:31:04 +02:00
+								<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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2011-02-08  Benjamin Kosnik  <bkoz@redhat.com>

	* doc/html/*: Regenerate.

From-SVN: r169960

											
										
										
											2011-02-09 02:45:25 +01:00
+								<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
-												status_cxx200x.xml: Update.

2011-02-10  Jonathan Wakely  <jwakely.gcc@gmail.com>

	* doc/xml/manual/status_cxx200x.xml: Update.
	* doc/html/*: Regenerate.

From-SVN: r169996

											
										
										
											2011-02-10 01:54:53 +01:00
+								<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Interacting with C</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.75.2"/><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="io.html" title="Chapter 13.  Input and Output"/><link rel="prev" href="fstreams.html" title="File Based Streams"/><link rel="next" href="atomics.html" title="Chapter 14.  Atomics"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Interacting with C</th></tr><tr><td align="left"><a accesskey="p" href="fstreams.html">Prev</a> </td><th width="60%" align="center">Chapter 13.
-												html: Regenerate.

2009-04-15  Benjamin Kosnik  <bkoz@redhat.com>

	* doc/html: Regenerate.

From-SVN: r146140

											
										
										
											2009-04-16 01:31:04 +02:00
+								  Input and Output
-												*: Regenerate.

2011-02-08  Benjamin Kosnik  <bkoz@redhat.com>

	* doc/html/*: Regenerate.

From-SVN: r169960

											
										
										
											2011-02-09 02:45:25 +01:00
+								</th><td align="right"> <a accesskey="n" href="atomics.html">Next</a></td></tr></table><hr/></div><div class="section" title="Interacting with C"><div class="titlepage"><div><div><h2 class="title"><a id="std.io.c"/>Interacting with C</h2></div></div></div><div class="section" title="Using FILE* and file descriptors"><div class="titlepage"><div><div><h3 class="title"><a id="std.io.c.FILE"/>Using FILE* and file descriptors</h3></div></div></div><p>
-												faq.xml: Link to manual.

2010-04-22  Jonathan Wakely  <jwakely.gcc@gmail.com>

	* doc/xml/faq.xml: Link to manual.
	* doc/xml/manual/using.xml: Expand dynamic libraries section.
	* doc/xml/manual/strings.xml: Mention shrink_to_fit() member.
	* doc/xml/manual/prerequisites.xml: Link to doxygen requirements.
	* doc/xml/manual/appendix_contributing.xml: Update Bash version.
	* doc/html/*: Regenerate.

From-SVN: r158624

											
										
										
											2010-04-22 01:33:44 +02:00
+								      See the <a class="link" href="ext_io.html" title="Chapter 26. Input and Output">extensions</a> for using
-												html: Regenerate.

2009-04-15  Benjamin Kosnik  <bkoz@redhat.com>

	* doc/html: Regenerate.

From-SVN: r146140

											
										
										
											2009-04-16 01:31:04 +02:00
+								      <span class="type">FILE</span> and <span class="type">file descriptors</span> with
 								      <code class="classname">ofstream</code> and
 								      <code class="classname">ifstream</code>.
-												*: Regenerate.

2011-02-08  Benjamin Kosnik  <bkoz@redhat.com>

	* doc/html/*: Regenerate.

From-SVN: r169960

											
										
										
											2011-02-09 02:45:25 +01:00
+								    </p></div><div class="section" title="Performance"><div class="titlepage"><div><div><h3 class="title"><a id="std.io.c.sync"/>Performance</h3></div></div></div><p>
-												faq.xml: Link to manual.

2010-04-22  Jonathan Wakely  <jwakely.gcc@gmail.com>

	* doc/xml/faq.xml: Link to manual.
	* doc/xml/manual/using.xml: Expand dynamic libraries section.
	* doc/xml/manual/strings.xml: Mention shrink_to_fit() member.
	* doc/xml/manual/prerequisites.xml: Link to doxygen requirements.
	* doc/xml/manual/appendix_contributing.xml: Update Bash version.
	* doc/html/*: Regenerate.

From-SVN: r158624

											
										
										
											2010-04-22 01:33:44 +02:00
+								      Pathetic Performance? Ditch C.
 								    </p><p>It sounds like a flame on C, but it isn't.  Really.  Calm down.
 								      I'm just saying it to get your attention.
 								   </p><p>Because the C++ library includes the C library, both C-style and
 								      C++-style I/O have to work at the same time.  For example:
 								   </p><pre class="programlisting">
 								     #include &lt;iostream&gt;
 								     #include &lt;cstdio&gt;
 								     std::cout &lt;&lt; "Hel";
 								     std::printf ("lo, worl");
 								     std::cout &lt;&lt; "d!\n";
 								   </pre><p>This must do what you think it does.
 								   </p><p>Alert members of the audience will immediately notice that buffering
 								      is going to make a hash of the output unless special steps are taken.
 								   </p><p>The special steps taken by libstdc++, at least for version 3.0,
 								      involve doing very little buffering for the standard streams, leaving
 								      most of the buffering to the underlying C library.  (This kind of
 								      thing is tricky to get right.)
 								      The upside is that correctness is ensured.  The downside is that
 								      writing through <code class="code">cout</code> can quite easily lead to awful
 								      performance when the C++ I/O library is layered on top of the C I/O
 								      library (as it is for 3.0 by default).  Some patches have been applied
 								      which improve the situation for 3.1.
 								   </p><p>However, the C and C++ standard streams only need to be kept in sync
 								      when both libraries' facilities are in use.  If your program only uses
 								      C++ I/O, then there's no need to sync with the C streams.  The right
 								      thing to do in this case is to call
 								   </p><pre class="programlisting">
 								     #include <span class="emphasis"><em>any of the I/O headers such as ios, iostream, etc</em></span>
 								     std::ios::sync_with_stdio(false);
 								   </pre><p>You must do this before performing any I/O via the C++ stream objects.
 								      Once you call this, the C++ streams will operate independently of the
 								      (unused) C streams.  For GCC 3.x, this means that <code class="code">cout</code> and
 								      company will become fully buffered on their own.
 								   </p><p>Note, by the way, that the synchronization requirement only applies to
 								      the standard streams (<code class="code">cin</code>, <code class="code">cout</code>,
 								      <code class="code">cerr</code>,
 								      <code class="code">clog</code>, and their wide-character counterchapters).  File stream
 								      objects that you declare yourself have no such requirement and are fully
 								      buffered.
-												*: Regenerate.

2011-02-08  Benjamin Kosnik  <bkoz@redhat.com>

	* doc/html/*: Regenerate.

From-SVN: r169960

											
										
										
											2011-02-09 02:45:25 +01:00
+								   </p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="fstreams.html">Prev</a> </td><td align="center"><a accesskey="u" href="io.html">Up</a></td><td align="right"> <a accesskey="n" href="atomics.html">Next</a></td></tr><tr><td align="left" valign="top">File Based Streams </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Chapter 14.
-												faq.xml: Link to manual.

2010-04-22  Jonathan Wakely  <jwakely.gcc@gmail.com>

	* doc/xml/faq.xml: Link to manual.
	* doc/xml/manual/using.xml: Expand dynamic libraries section.
	* doc/xml/manual/strings.xml: Mention shrink_to_fit() member.
	* doc/xml/manual/prerequisites.xml: Link to doxygen requirements.
	* doc/xml/manual/appendix_contributing.xml: Update Bash version.
	* doc/html/*: Regenerate.

From-SVN: r158624

											
										
										
											2010-04-22 01:33:44 +02:00
+								  Atomics
 								</td></tr></table></div></body></html>