libstdc++-v3/docs/html/explanations.html

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   3    <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" />
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   5    <meta name="DESCRIPTION" content="Explanatory notes about libstdc++-v3." />
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   7    <title>Explanatory notes about libstdc++-v3 design</title>
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  12 <h1 class="centered"><a name="top">Explanatory notes about libstdc++-v3
  13 design</a></h1>
  14
  15 <p>The latest version of this document is always available at
  16    <a href="http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html">
  17    http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html</a>.
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  20 <p>To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
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  26 <h3><a name="cstdio">&quot;I/O packages&quot;, <code>--enable-cstdio</code></a></h3>
  27 <p>In addition to all the nifty things which C++ can do for I/O, its library
  28    also includes all of the I/O capabilites of C.  Making them work together
  29    can be a challenge, not only
  30    <a href="27_io/howto.html#8">for the programmer</a> but for the
  31    implementors as well.
  32 </p>
  33 <p>There are two ways to do a C++ library:  the cool way, and the easy way.
  34    More specifically, the cool-but-easy-to-get-wrong way, and the
  35    easy-to-guarantee-correct-behavior way.  For 3.0, the easy way is used.
  36 </p>
  37 <p>Choosing 'stdio' is the easy way.  It builds a C++ library which forwards
  38    all operations to the C library.  Many of the C++ I/O functions are
  39    specified in the standard 'as if' they called a certain C function; the
  40    easiest way to get it correct is to actually call that function.  The
  41    disadvantage is that the C++ code will run slower (fortunately, the layer
  42    is thin).
  43 </p>
  44 <p>Choosing 'libio' is the cool way; it allows C++ and C to share some
  45    buffers.  It's disabled because of tricky synchronization issues.  Other
  46    cool ways (various methods of sharing resources between C and C++
  47    facilities, instead of layering) are possible.  This approach can speed
  48    up I/O significantly.
  49 </p>
  50 <p>Other packages are possible.  For a new package, a header must be
  51    written to provide types like streamsize (usually just a typedef), as
  52    well as some internal types like<code> __c_file_type </code> and
  53    <code> __c_lock </code> (for the stdio case, these are FILE (as in
  54    &quot;FILE*&quot;) and a simple POSIX mutex, respectively).  An
  55    interface class called <code> __basic_file </code> must also be filled in;
  56    as an example, for the stdio case, these member functions are all
  57    inline calles to fread, fwrite, etc.
  58 </p>
  59 <p>Return <a href="#top">to the top of the page</a> or
  60    <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
  61 </p>
  62
  63
  64 <hr />
  65 <h3><a name="alloc">Internal Allocators</a></h3>
  66 <p>
  67 </p>
  68 <p>Return <a href="#top">to the top of the page</a> or
  69    <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
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  76 <p class="fineprint"><em>
  77 See <a href="17_intro/license.html">license.html</a> for copying conditions.
  78 Comments and suggestions are welcome, and may be sent to
  79 <a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
  80 </em></p>
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