mirror of git://gcc.gnu.org/git/gcc.git
85 lines
3.3 KiB
HTML
85 lines
3.3 KiB
HTML
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<meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)">
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<meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++">
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<meta name="DESCRIPTION" content="Explanatory notes about libstdc++-v3.">
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<meta name="GENERATOR" content="vi and eight fingers">
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<title>Explanatory notes about libstdc++-v3 design</title>
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<link rel="StyleSheet" href="lib3styles.css">
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<h1 class="centered"><a name="top">Explanatory notes about libstdc++-v3
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design</a></h1>
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<p>The latest version of this document is always available at
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<a href="http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html">
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http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html</a>.
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</p>
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<p>To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
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<hr>
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<a name="cstdio"><h3>"I/O packages", <code>--enable-cstdio</code></h3></a>
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<p>In addition to all the nifty things which C++ can do for I/O, its library
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also includes all of the I/O capabilites of C. Making them work together
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can be a challenge, not only
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<a href="27_io/howto.html#8">for the programmer</a> but for the
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implementors as well.
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</p>
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<p>There are two ways to do a C++ library: the cool way, and the easy way.
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More specifically, the cool-but-easy-to-get-wrong way, and the
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easy-to-guarantee-correct-behavior way. For 3.0, the easy way is used.
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</p>
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<p>Choosing 'stdio' is the easy way. It builds a C++ library which forwards
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all operations to the C library. Many of the C++ I/O functions are
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specified in the standard 'as if' they called a certain C function; the
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easiest way to get it correct is to actually call that function. The
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disadvantage is that the C++ code will run slower (fortunately, the layer
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is thin).
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</p>
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<p>Choosing 'libio' is the cool way; it allows C++ and C to share some
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buffers. It's disabled because of tricky synchronization issues. Other
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cool ways (various methods of sharing resources between C and C++
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facilities, instead of layering) are possible. This approach can speed
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up I/O significantly.
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</p>
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<p>Other packages are possible. For a new package, a header must be
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written to provide types like streamsize (usually just a typedef), as
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well as some internal types like<code> __c_file_type </code> and
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<code> __c_lock </code> (for the stdio case, these are FILE (as in
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"FILE*") and a simple POSIX mutex, respectively). An
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interface class called <code> __basic_file </code> must also be filled in;
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as an example, for the stdio case, these member functions are all
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inline calles to fread, fwrite, etc.
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</p>
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<p>Return <a href="#top">to the top of the page</a> or
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<a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
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</p>
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<hr>
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<a name="alloc"><h3>Internal Allocators</h3></a>
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<p>
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</p>
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<p>Return <a href="#top">to the top of the page</a> or
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<a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
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</p>
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<hr>
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<p class="fineprint"><em>
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See <a href="17_intro/license.html">license.html</a> for copying conditions.
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Comments and suggestions are welcome, and may be sent to
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<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
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</em></p>
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</body>
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</html>
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