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<meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" />
<meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++" />
<meta name="DESCRIPTION" content="Explanatory notes about libstdc++-v3." />
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<title>Explanatory notes about libstdc++-v3 design</title>
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<h1 class="centered"><a name="top">Explanatory notes about libstdc++-v3
design</a></h1>
<p class="fineprint"><em>
The latest version of this document is always available at
<a href="http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html">
http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html</a>.
</em></p>
<p><em>
To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
</em></p>
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<h3><a name="cstdio">"I/O packages", <code>--enable-cstdio</code></a></h3>
<p>In addition to all the nifty things which C++ can do for I/O, its library
also includes all of the I/O capabilites of C. Making them work together
can be a challenge, not only
<a href="27_io/howto.html#8">for the programmer</a> but for the
implementors as well.
</p>
<p>There are two ways to do a C++ library: the cool way, and the easy way.
More specifically, the cool-but-easy-to-get-wrong way, and the
easy-to-guarantee-correct-behavior way. For 3.0, the easy way is used.
</p>
<p>Choosing 'stdio' is the easy way. It builds a C++ library which forwards
all operations to the C library. Many of the C++ I/O functions are
specified in the standard 'as if' they called a certain C function; the
easiest way to get it correct is to actually call that function. The
disadvantage is that the C++ code will run slower (fortunately, the layer
is thin).
</p>
<p>Other packages are possible. For a new package, a header must be
written to provide types like streamsize (usually just a typedef), as
well as some internal types like<code> __c_file_type </code> and
<code> __c_lock </code> (for the stdio case, these are FILE (as in
"FILE*") and a simple POSIX mutex, respectively). An
interface class called <code> __basic_file </code> must also be filled in;
as an example, for the stdio case, these member functions are all
inline calles to fread, fwrite, etc.
</p>
<p>Return <a href="#top">to the top of the page</a> or
<a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
</p>
<hr />
<h3><a name="alloc">Internal Allocators</a></h3>
<p>
</p>
<p>Return <a href="#top">to the top of the page</a> or
<a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
</p>
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<p class="fineprint"><em>
See <a href="17_intro/license.html">license.html</a> for copying conditions.
Comments and suggestions are welcome, and may be sent to
<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
</em></p>
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