--- /dev/null
+<?xml version='1.0'?>
+<!DOCTYPE part PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
+[ ]>
+
+<part id="manual.io" xreflabel="Input and Output">
+<?dbhtml filename="io.html"?>
+
+<partinfo>
+ <keywordset>
+ <keyword>
+ ISO C++
+ </keyword>
+ <keyword>
+ library
+ </keyword>
+ </keywordset>
+</partinfo>
+
+<title>
+ Input and Output
+ <indexterm><primary>Input and Output</primary></indexterm>
+</title>
+
+<!-- Chapter 01 : Iostream Objects -->
+<chapter id="manual.io.objects" xreflabel="IO Objects">
+<?dbhtml filename="iostream_objects.html"?>
+ <title>Iostream Objects</title>
+
+ <para>To minimize the time you have to wait on the compiler, it's good to
+ only include the headers you really need. Many people simply include
+ <iostream> when they don't need to -- and that can <emphasis>penalize
+ your runtime as well.</emphasis> Here are some tips on which header to use
+ for which situations, starting with the simplest.
+ </para>
+ <para><emphasis><iosfwd></emphasis> should be included whenever you simply
+ need the <emphasis>name</emphasis> of an I/O-related class, such as
+ "ofstream" or "basic_streambuf". Like the name
+ implies, these are forward declarations. (A word to all you fellow
+ old school programmers: trying to forward declare classes like
+ "class istream;" won't work. Look in the iosfwd header if
+ you'd like to know why.) For example,
+ </para>
+ <programlisting>
+ #include <iosfwd>
+
+ class MyClass
+ {
+ ....
+ std::ifstream& input_file;
+ };
+
+ extern std::ostream& operator<< (std::ostream&, MyClass&);
+ </programlisting>
+ <para><emphasis><ios></emphasis> declares the base classes for the entire
+ I/O stream hierarchy, std::ios_base and std::basic_ios<charT>, the
+ counting types std::streamoff and std::streamsize, the file
+ positioning type std::fpos, and the various manipulators like
+ std::hex, std::fixed, std::noshowbase, and so forth.
+ </para>
+ <para>The ios_base class is what holds the format flags, the state flags,
+ and the functions which change them (setf(), width(), precision(),
+ etc). You can also store extra data and register callback functions
+ through ios_base, but that has been historically underused. Anything
+ which doesn't depend on the type of characters stored is consolidated
+ here.
+ </para>
+ <para>The template class basic_ios is the highest template class in the
+ hierarchy; it is the first one depending on the character type, and
+ holds all general state associated with that type: the pointer to the
+ polymorphic stream buffer, the facet information, etc.
+ </para>
+ <para><emphasis><streambuf></emphasis> declares the template class
+ basic_streambuf, and two standard instantiations, streambuf and
+ wstreambuf. If you need to work with the vastly useful and capable
+ stream buffer classes, e.g., to create a new form of storage
+ transport, this header is the one to include.
+ </para>
+ <para><emphasis><istream></emphasis>/<emphasis><ostream></emphasis> are
+ the headers to include when you are using the >>/<<
+ interface, or any of the other abstract stream formatting functions.
+ For example,
+ </para>
+ <programlisting>
+ #include <istream>
+
+ std::ostream& operator<< (std::ostream& os, MyClass& c)
+ {
+ return os << c.data1() << c.data2();
+ }
+ </programlisting>
+ <para>The std::istream and std::ostream classes are the abstract parents of
+ the various concrete implementations. If you are only using the
+ interfaces, then you only need to use the appropriate interface header.
+ </para>
+ <para><emphasis><iomanip></emphasis> provides "extractors and inserters
+ that alter information maintained by class ios_base and its derived
+ classes," such as std::setprecision and std::setw. If you need
+ to write expressions like <code>os << setw(3);</code> or
+ <code>is >> setbase(8);</code>, you must include <iomanip>.
+ </para>
+ <para><emphasis><sstream></emphasis>/<emphasis><fstream></emphasis>
+ declare the six stringstream and fstream classes. As they are the
+ standard concrete descendants of istream and ostream, you will already
+ know about them.
+ </para>
+ <para>Finally, <emphasis><iostream></emphasis> provides the eight standard
+ global objects (cin, cout, etc). To do this correctly, this header
+ also provides the contents of the <istream> and <ostream>
+ headers, but nothing else. The contents of this header look like
+ </para>
+ <programlisting>
+ #include <ostream>
+ #include <istream>
+
+ namespace std
+ {
+ extern istream cin;
+ extern ostream cout;
+ ....
+
+ // this is explained below
+ <emphasis>static ios_base::Init __foo;</emphasis> // not its real name
+ }
+ </programlisting>
+ <para>Now, the runtime penalty mentioned previously: the global objects
+ must be initialized before any of your own code uses them; this is
+ guaranteed by the standard. Like any other global object, they must
+ be initialized once and only once. This is typically done with a
+ construct like the one above, and the nested class ios_base::Init is
+ specified in the standard for just this reason.
+ </para>
+ <para>How does it work? Because the header is included before any of your
+ code, the <emphasis>__foo</emphasis> object is constructed before any of
+ your objects. (Global objects are built in the order in which they
+ are declared, and destroyed in reverse order.) The first time the
+ constructor runs, the eight stream objects are set up.
+ </para>
+ <para>The <code>static</code> keyword means that each object file compiled
+ from a source file containing <iostream> will have its own
+ private copy of <emphasis>__foo</emphasis>. There is no specified order
+ of construction across object files (it's one of those pesky NP
+ problems that make life so interesting), so one copy in each object
+ file means that the stream objects are guaranteed to be set up before
+ any of your code which uses them could run, thereby meeting the
+ requirements of the standard.
+ </para>
+ <para>The penalty, of course, is that after the first copy of
+ <emphasis>__foo</emphasis> is constructed, all the others are just wasted
+ processor time. The time spent is merely for an increment-and-test
+ inside a function call, but over several dozen or hundreds of object
+ files, that time can add up. (It's not in a tight loop, either.)
+ </para>
+ <para>The lesson? Only include <iostream> when you need to use one of
+ the standard objects in that source file; you'll pay less startup
+ time. Only include the header files you need to in general; your
+ compile times will go down when there's less parsing work to do.
+ </para>
+
+</chapter>
+
+<!-- Chapter 02 : Stream Buffers -->
+<chapter id="manual.io.streambufs" xreflabel="Stream Buffers">
+<?dbhtml filename="streambufs.html"?>
+ <title>Stream Buffers</title>
+
+ <sect1 id="io.streambuf.derived" xreflabel="Derived streambuf Classes">
+ <title>Derived streambuf Classes</title>
+ <para>
+ </para>
+
+ <para>Creating your own stream buffers for I/O can be remarkably easy.
+ If you are interested in doing so, we highly recommend two very
+ excellent books:
+ <ulink url="http://www.langer.camelot.de/iostreams.html">Standard C++
+ IOStreams and Locales</ulink> by Langer and Kreft, ISBN 0-201-18395-1, and
+ <ulink url="http://www.josuttis.com/libbook/">The C++ Standard Library</ulink>
+ by Nicolai Josuttis, ISBN 0-201-37926-0. Both are published by
+ Addison-Wesley, who isn't paying us a cent for saying that, honest.
+ </para>
+ <para>Here is a simple example, io/outbuf1, from the Josuttis text. It
+ transforms everything sent through it to uppercase. This version
+ assumes many things about the nature of the character type being
+ used (for more information, read the books or the newsgroups):
+ </para>
+ <programlisting>
+ #include <iostream>
+ #include <streambuf>
+ #include <locale>
+ #include <cstdio>
+
+ class outbuf : public std::streambuf
+ {
+ protected:
+ /* central output function
+ * - print characters in uppercase mode
+ */
+ virtual int_type overflow (int_type c) {
+ if (c != EOF) {
+ // convert lowercase to uppercase
+ c = std::toupper(static_cast<char>(c),getloc());
+
+ // and write the character to the standard output
+ if (putchar(c) == EOF) {
+ return EOF;
+ }
+ }
+ return c;
+ }
+ };
+
+ int main()
+ {
+ // create special output buffer
+ outbuf ob;
+ // initialize output stream with that output buffer
+ std::ostream out(&ob);
+
+ out << "31 hexadecimal: "
+ << std::hex << 31 << std::endl;
+ return 0;
+ }
+ </programlisting>
+ <para>Try it yourself! More examples can be found in 3.1.x code, in
+ <code>include/ext/*_filebuf.h</code>, and on
+ <ulink url="http://www.informatik.uni-konstanz.de/~kuehl/c++/iostream/">Dietmar
+ Kühl's IOStreams page</ulink>.
+ </para>
+
+ </sect1>
+
+ <sect1 id="io.streambuf.buffering" xreflabel="Buffering">
+ <title>Buffering</title>
+ <para>First, are you sure that you understand buffering? Particularly
+ the fact that C++ may not, in fact, have anything to do with it?
+ </para>
+ <para>The rules for buffering can be a little odd, but they aren't any
+ different from those of C. (Maybe that's why they can be a bit
+ odd.) Many people think that writing a newline to an output
+ stream automatically flushes the output buffer. This is true only
+ when the output stream is, in fact, a terminal and not a file
+ or some other device -- and <emphasis>that</emphasis> may not even be true
+ since C++ says nothing about files nor terminals. All of that is
+ system-dependent. (The "newline-buffer-flushing only occurring
+ on terminals" thing is mostly true on Unix systems, though.)
+ </para>
+ <para>Some people also believe that sending <code>endl</code> down an
+ output stream only writes a newline. This is incorrect; after a
+ newline is written, the buffer is also flushed. Perhaps this
+ is the effect you want when writing to a screen -- get the text
+ out as soon as possible, etc -- but the buffering is largely
+ wasted when doing this to a file:
+ </para>
+ <programlisting>
+ output << "a line of text" << endl;
+ output << some_data_variable << endl;
+ output << "another line of text" << endl; </programlisting>
+ <para>The proper thing to do in this case to just write the data out
+ and let the libraries and the system worry about the buffering.
+ If you need a newline, just write a newline:
+ </para>
+ <programlisting>
+ output << "a line of text\n"
+ << some_data_variable << '\n'
+ << "another line of text\n"; </programlisting>
+ <para>I have also joined the output statements into a single statement.
+ You could make the code prettier by moving the single newline to
+ the start of the quoted text on the last line, for example.
+ </para>
+ <para>If you do need to flush the buffer above, you can send an
+ <code>endl</code> if you also need a newline, or just flush the buffer
+ yourself:
+ </para>
+ <programlisting>
+ output << ...... << flush; // can use std::flush manipulator
+ output.flush(); // or call a member fn </programlisting>
+ <para>On the other hand, there are times when writing to a file should
+ be like writing to standard error; no buffering should be done
+ because the data needs to appear quickly (a prime example is a
+ log file for security-related information). The way to do this is
+ just to turn off the buffering <emphasis>before any I/O operations at
+ all</emphasis> have been done (note that opening counts as an I/O operation):
+ </para>
+ <programlisting>
+ std::ofstream os;
+ std::ifstream is;
+ int i;
+
+ os.rdbuf()->pubsetbuf(0,0);
+ is.rdbuf()->pubsetbuf(0,0);
+
+ os.open("/foo/bar/baz");
+ is.open("/qux/quux/quuux");
+ ...
+ os << "this data is written immediately\n";
+ is >> i; // and this will probably cause a disk read </programlisting>
+ <para>Since all aspects of buffering are handled by a streambuf-derived
+ member, it is necessary to get at that member with <code>rdbuf()</code>.
+ Then the public version of <code>setbuf</code> can be called. The
+ arguments are the same as those for the Standard C I/O Library
+ function (a buffer area followed by its size).
+ </para>
+ <para>A great deal of this is implementation-dependent. For example,
+ <code>streambuf</code> does not specify any actions for its own
+ <code>setbuf()</code>-ish functions; the classes derived from
+ <code>streambuf</code> each define behavior that "makes
+ sense" for that class: an argument of (0,0) turns off buffering
+ for <code>filebuf</code> but does nothing at all for its siblings
+ <code>stringbuf</code> and <code>strstreambuf</code>, and specifying
+ anything other than (0,0) has varying effects.
+ User-defined classes derived from <code>streambuf</code> can
+ do whatever they want. (For <code>filebuf</code> and arguments for
+ <code>(p,s)</code> other than zeros, libstdc++ does what you'd expect:
+ the first <code>s</code> bytes of <code>p</code> are used as a buffer,
+ which you must allocate and deallocate.)
+ </para>
+ <para>A last reminder: there are usually more buffers involved than
+ just those at the language/library level. Kernel buffers, disk
+ buffers, and the like will also have an effect. Inspecting and
+ changing those are system-dependent.
+ </para>
+
+ </sect1>
+</chapter>
+
+<!-- Chapter 03 : Memory-based Streams -->
+<chapter id="manual.io.memstreams" xreflabel="Memory Streams">
+<?dbhtml filename="stringstreams.html"?>
+ <title>Memory Based Streams</title>
+ <sect1 id="manual.io.memstreams.compat" xreflabel="Compatibility strstream">
+ <title>Compatibility With strstream</title>
+ <para>
+ </para>
+ <para>Stringstreams (defined in the header <code><sstream></code>)
+ are in this author's opinion one of the coolest things since
+ sliced time. An example of their use is in the Received Wisdom
+ section for Chapter 21 (Strings),
+ <ulink url="../21_strings/howto.html#1.1internal"> describing how to
+ format strings</ulink>.
+ </para>
+ <para>The quick definition is: they are siblings of ifstream and ofstream,
+ and they do for <code>std::string</code> what their siblings do for
+ files. All that work you put into writing <code><<</code> and
+ <code>>></code> functions for your classes now pays off
+ <emphasis>again!</emphasis> Need to format a string before passing the string
+ to a function? Send your stuff via <code><<</code> to an
+ ostringstream. You've read a string as input and need to parse it?
+ Initialize an istringstream with that string, and then pull pieces
+ out of it with <code>>></code>. Have a stringstream and need to
+ get a copy of the string inside? Just call the <code>str()</code>
+ member function.
+ </para>
+ <para>This only works if you've written your
+ <code><<</code>/<code>>></code> functions correctly, though,
+ and correctly means that they take istreams and ostreams as
+ parameters, not i<emphasis>f</emphasis>streams and o<emphasis>f</emphasis>streams. If they
+ take the latter, then your I/O operators will work fine with
+ file streams, but with nothing else -- including stringstreams.
+ </para>
+ <para>If you are a user of the strstream classes, you need to update
+ your code. You don't have to explicitly append <code>ends</code> to
+ terminate the C-style character array, you don't have to mess with
+ "freezing" functions, and you don't have to manage the
+ memory yourself. The strstreams have been officially deprecated,
+ which means that 1) future revisions of the C++ Standard won't
+ support them, and 2) if you use them, people will laugh at you.
+ </para>
+
+
+ </sect1>
+</chapter>
+
+<!-- Chapter 04 : File-based Streams -->
+<chapter id="manual.io.filestreams" xreflabel="File Streams">
+<?dbhtml filename="fstreams.html"?>
+ <title>File Based Streams</title>
+
+ <sect1 id="manual.io.filestreams.copying_a_file" xreflabel="Copying a File">
+ <title>Copying a File</title>
+ <para>
+ </para>
+
+ <para>So you want to copy a file quickly and easily, and most important,
+ completely portably. And since this is C++, you have an open
+ ifstream (call it IN) and an open ofstream (call it OUT):
+ </para>
+ <programlisting>
+ #include <fstream>
+
+ std::ifstream IN ("input_file");
+ std::ofstream OUT ("output_file"); </programlisting>
+ <para>Here's the easiest way to get it completely wrong:
+ </para>
+ <programlisting>
+ OUT << IN;</programlisting>
+ <para>For those of you who don't already know why this doesn't work
+ (probably from having done it before), I invite you to quickly
+ create a simple text file called "input_file" containing
+ the sentence
+ </para>
+ <programlisting>
+ The quick brown fox jumped over the lazy dog.</programlisting>
+ <para>surrounded by blank lines. Code it up and try it. The contents
+ of "output_file" may surprise you.
+ </para>
+ <para>Seriously, go do it. Get surprised, then come back. It's worth it.
+ </para>
+ <para>The thing to remember is that the <code>basic_[io]stream</code> classes
+ handle formatting, nothing else. In particular, they break up on
+ whitespace. The actual reading, writing, and storing of data is
+ handled by the <code>basic_streambuf</code> family. Fortunately, the
+ <code>operator<<</code> is overloaded to take an ostream and
+ a pointer-to-streambuf, in order to help with just this kind of
+ "dump the data verbatim" situation.
+ </para>
+ <para>Why a <emphasis>pointer</emphasis> to streambuf and not just a streambuf? Well,
+ the [io]streams hold pointers (or references, depending on the
+ implementation) to their buffers, not the actual
+ buffers. This allows polymorphic behavior on the part of the buffers
+ as well as the streams themselves. The pointer is easily retrieved
+ using the <code>rdbuf()</code> member function. Therefore, the easiest
+ way to copy the file is:
+ </para>
+ <programlisting>
+ OUT << IN.rdbuf();</programlisting>
+ <para>So what <emphasis>was</emphasis> happening with OUT<<IN? Undefined
+ behavior, since that particular << isn't defined by the Standard.
+ I have seen instances where it is implemented, but the character
+ extraction process removes all the whitespace, leaving you with no
+ blank lines and only "Thequickbrownfox...". With
+ libraries that do not define that operator, IN (or one of IN's
+ member pointers) sometimes gets converted to a void*, and the output
+ file then contains a perfect text representation of a hexadecimal
+ address (quite a big surprise). Others don't compile at all.
+ </para>
+ <para>Also note that none of this is specific to o<emphasis>*f*</emphasis>streams.
+ The operators shown above are all defined in the parent
+ basic_ostream class and are therefore available with all possible
+ descendants.
+ </para>
+
+ </sect1>
+
+ <sect1 id="manual.io.filestreams.binary" xreflabel="Binary Input and Output">
+ <title>Binary Input and Output</title>
+ <para>
+ </para>
+ <para>The first and most important thing to remember about binary I/O is
+ that opening a file with <code>ios::binary</code> is not, repeat
+ <emphasis>not</emphasis>, the only thing you have to do. It is not a silver
+ bullet, and will not allow you to use the <code><</>></code>
+ operators of the normal fstreams to do binary I/O.
+ </para>
+ <para>Sorry. Them's the breaks.
+ </para>
+ <para>This isn't going to try and be a complete tutorial on reading and
+ writing binary files (because "binary"
+ <ulink url="#7">covers a lot of ground)</ulink>, but we will try and clear
+ up a couple of misconceptions and common errors.
+ </para>
+ <para>First, <code>ios::binary</code> has exactly one defined effect, no more
+ and no less. Normal text mode has to be concerned with the newline
+ characters, and the runtime system will translate between (for
+ example) '\n' and the appropriate end-of-line sequence (LF on Unix,
+ CRLF on DOS, CR on Macintosh, etc). (There are other things that
+ normal mode does, but that's the most obvious.) Opening a file in
+ binary mode disables this conversion, so reading a CRLF sequence
+ under Windows won't accidentally get mapped to a '\n' character, etc.
+ Binary mode is not supposed to suddenly give you a bitstream, and
+ if it is doing so in your program then you've discovered a bug in
+ your vendor's compiler (or some other part of the C++ implementation,
+ possibly the runtime system).
+ </para>
+ <para>Second, using <code><<</code> to write and <code>>></code> to
+ read isn't going to work with the standard file stream classes, even
+ if you use <code>skipws</code> during reading. Why not? Because
+ ifstream and ofstream exist for the purpose of <emphasis>formatting</emphasis>,
+ not reading and writing. Their job is to interpret the data into
+ text characters, and that's exactly what you don't want to happen
+ during binary I/O.
+ </para>
+ <para>Third, using the <code>get()</code> and <code>put()/write()</code> member
+ functions still aren't guaranteed to help you. These are
+ "unformatted" I/O functions, but still character-based.
+ (This may or may not be what you want, see below.)
+ </para>
+ <para>Notice how all the problems here are due to the inappropriate use
+ of <emphasis>formatting</emphasis> functions and classes to perform something
+ which <emphasis>requires</emphasis> that formatting not be done? There are a
+ seemingly infinite number of solutions, and a few are listed here:
+ </para>
+ <itemizedlist>
+ <listitem>
+ <para><quote>Derive your own fstream-type classes and write your own
+ <</>> operators to do binary I/O on whatever data
+ types you're using.</quote>
+ </para>
+ <para>
+ This is a Bad Thing, because while
+ the compiler would probably be just fine with it, other humans
+ are going to be confused. The overloaded bitshift operators
+ have a well-defined meaning (formatting), and this breaks it.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <quote>Build the file structure in memory, then
+ <code>mmap()</code> the file and copy the
+ structure.
+ </quote>
+ </para>
+ <para>
+ Well, this is easy to make work, and easy to break, and is
+ pretty equivalent to using <code>::read()</code> and
+ <code>::write()</code> directly, and makes no use of the
+ iostream library at all...
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <quote>Use streambufs, that's what they're there for.</quote>
+ </para>
+ <para>
+ While not trivial for the beginner, this is the best of all
+ solutions. The streambuf/filebuf layer is the layer that is
+ responsible for actual I/O. If you want to use the C++
+ library for binary I/O, this is where you start.
+ </para>
+ </listitem>
+ </itemizedlist>
+ <para>How to go about using streambufs is a bit beyond the scope of this
+ document (at least for now), but while streambufs go a long way,
+ they still leave a couple of things up to you, the programmer.
+ As an example, byte ordering is completely between you and the
+ operating system, and you have to handle it yourself.
+ </para>
+ <para>Deriving a streambuf or filebuf
+ class from the standard ones, one that is specific to your data
+ types (or an abstraction thereof) is probably a good idea, and
+ lots of examples exist in journals and on Usenet. Using the
+ standard filebufs directly (either by declaring your own or by
+ using the pointer returned from an fstream's <code>rdbuf()</code>)
+ is certainly feasible as well.
+ </para>
+ <para>One area that causes problems is trying to do bit-by-bit operations
+ with filebufs. C++ is no different from C in this respect: I/O
+ must be done at the byte level. If you're trying to read or write
+ a few bits at a time, you're going about it the wrong way. You
+ must read/write an integral number of bytes and then process the
+ bytes. (For example, the streambuf functions take and return
+ variables of type <code>int_type</code>.)
+ </para>
+ <para>Another area of problems is opening text files in binary mode.
+ Generally, binary mode is intended for binary files, and opening
+ text files in binary mode means that you now have to deal with all of
+ those end-of-line and end-of-file problems that we mentioned before.
+ An instructive thread from comp.lang.c++.moderated delved off into
+ this topic starting more or less at
+ <ulink url="http://groups.google.com/groups?oi=djq&selm=an_436187505">this</ulink>
+ article and continuing to the end of the thread. (You'll have to
+ sort through some flames every couple of paragraphs, but the points
+ made are good ones.)
+ </para>
+
+ </sect1>
+
+ <sect1 id="manual.io.filestreams.binary2" xreflabel="Binary Input and Output">
+ <title>More Binary Input and Output</title>
+ <para>Towards the beginning of February 2001, the subject of
+ "binary" I/O was brought up in a couple of places at the
+ same time. One notable place was Usenet, where James Kanze and
+ Dietmar Kühl separately posted articles on why attempting
+ generic binary I/O was not a good idea. (Here are copies of
+ <ulink url="binary_iostreams_kanze.txt">Kanze's article</ulink> and
+ <ulink url="binary_iostreams_kuehl.txt">Kühl's article</ulink>.)
+ </para>
+ <para>Briefly, the problems of byte ordering and type sizes mean that
+ the unformatted functions like <code>ostream::put()</code> and
+ <code>istream::get()</code> cannot safely be used to communicate
+ between arbitrary programs, or across a network, or from one
+ invocation of a program to another invocation of the same program
+ on a different platform, etc.
+ </para>
+ <para>The entire Usenet thread is instructive, and took place under the
+ subject heading "binary iostreams" on both comp.std.c++
+ and comp.lang.c++.moderated in parallel. Also in that thread,
+ Dietmar Kühl mentioned that he had written a pair of stream
+ classes that would read and write XDR, which is a good step towards
+ a portable binary format.
+ </para>
+
+ </sect1>
+
+</chapter>
+
+<!-- Chapter 03 : Interacting with C -->
+<chapter id="manual.io.c" xreflabel="Interacting with C">
+<?dbhtml filename="io_and_c.html"?>
+ <title>Interacting with C</title>
+
+
+ <sect1 id="manual.io.c.FILE" xreflabel="Using FILE* and file descriptors">
+ <title>Using FILE* and file descriptors</title>
+ <para>
+ See the <link linkend="manual.ext.io">extensions</link> for using
+ <type>FILE</type> and <type>file descriptors</type> with
+ <classname>ofstream</classname> and
+ <classname>ifstream</classname>.
+ </para>
+ </sect1>
+
+ <sect1 id="manual.io.c.sync" xreflabel="Performance Issues">
+ <title>Performance</title>
+ <para>
+ Pathetic Performance? Ditch C.
+ </para>
+ <para>It sounds like a flame on C, but it isn't. Really. Calm down.
+ I'm just saying it to get your attention.
+ </para>
+ <para>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:
+ </para>
+ <programlisting>
+ #include <iostream>
+ #include <cstdio>
+
+ std::cout << "Hel";
+ std::printf ("lo, worl");
+ std::cout << "d!\n";
+ </programlisting>
+ <para>This must do what you think it does.
+ </para>
+ <para>Alert members of the audience will immediately notice that buffering
+ is going to make a hash of the output unless special steps are taken.
+ </para>
+ <para>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>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.
+ </para>
+ <para>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
+ </para>
+ <programlisting>
+ #include <emphasis>any of the I/O headers such as ios, iostream, etc</emphasis>
+
+ std::ios::sync_with_stdio(false);
+ </programlisting>
+ <para>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>cout</code> and
+ company will become fully buffered on their own.
+ </para>
+ <para>Note, by the way, that the synchronization requirement only applies to
+ the standard streams (<code>cin</code>, <code>cout</code>,
+ <code>cerr</code>,
+ <code>clog</code>, and their wide-character counterparts). File stream
+ objects that you declare yourself have no such requirement and are fully
+ buffered.
+ </para>
+
+
+ </sect1>
+</chapter>
+
+</part>
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