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| 6 | <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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| 7 | <head>
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| 8 | <meta name="AUTHOR" content="[email protected] (Phil Edwards)" />
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| 9 | <meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++" />
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| 10 | <meta name="DESCRIPTION" content="Explanatory notes about libstdc++-v3." />
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| 11 | <meta name="GENERATOR" content="vi and eight fingers" />
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| 12 | <title>Explanatory notes about libstdc++-v3 design</title>
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| 13 | <link rel="StyleSheet" href="lib3styles.css" />
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| 14 | </head>
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| 15 | <body>
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| 16 |
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| 17 | <h1 class="centered"><a name="top">Explanatory notes about libstdc++-v3
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| 18 | design</a></h1>
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| 19 |
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| 20 | <p>The latest version of this document is always available at
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| 21 | <a href="http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html">
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| 22 | http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html</a>.
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| 23 | </p>
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| 24 |
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| 25 | <p>To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
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| 26 | </p>
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| 27 |
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| 28 |
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| 29 | <!-- ####################################################### -->
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| 30 | <hr />
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| 31 | <h3><a name="cstdio">"I/O packages", <code>--enable-cstdio</code></a></h3>
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| 32 | <p>In addition to all the nifty things which C++ can do for I/O, its library
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| 33 | also includes all of the I/O capabilites of C. Making them work together
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| 34 | can be a challenge, not only
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| 35 | <a href="27_io/howto.html#8">for the programmer</a> but for the
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| 36 | implementors as well.
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| 37 | </p>
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| 38 | <p>There are two ways to do a C++ library: the cool way, and the easy way.
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| 39 | More specifically, the cool-but-easy-to-get-wrong way, and the
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| 40 | easy-to-guarantee-correct-behavior way. For 3.0, the easy way is used.
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| 41 | </p>
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| 42 | <p>Choosing 'stdio' is the easy way. It builds a C++ library which forwards
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| 43 | all operations to the C library. Many of the C++ I/O functions are
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| 44 | specified in the standard 'as if' they called a certain C function; the
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| 45 | easiest way to get it correct is to actually call that function. The
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| 46 | disadvantage is that the C++ code will run slower (fortunately, the layer
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| 47 | is thin).
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| 48 | </p>
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| 49 | <p>Choosing 'libio' is the cool way; it allows C++ and C to share some
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| 50 | buffers. It's disabled because of tricky synchronization issues. Other
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| 51 | cool ways (various methods of sharing resources between C and C++
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| 52 | facilities, instead of layering) are possible. This approach can speed
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| 53 | up I/O significantly.
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| 54 | </p>
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| 55 | <p>Other packages are possible. For a new package, a header must be
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| 56 | written to provide types like streamsize (usually just a typedef), as
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| 57 | well as some internal types like<code> __c_file_type </code> and
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| 58 | <code> __c_lock </code> (for the stdio case, these are FILE (as in
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| 59 | "FILE*") and a simple POSIX mutex, respectively). An
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| 60 | interface class called <code> __basic_file </code> must also be filled in;
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| 61 | as an example, for the stdio case, these member functions are all
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| 62 | inline calles to fread, fwrite, etc.
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| 63 | </p>
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| 64 | <p>Return <a href="#top">to the top of the page</a> or
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| 65 | <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
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| 66 | </p>
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| 67 |
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| 68 |
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| 69 | <hr />
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| 70 | <h3><a name="alloc">Internal Allocators</a></h3>
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| 71 | <p>
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| 72 | </p>
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| 73 | <p>Return <a href="#top">to the top of the page</a> or
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| 74 | <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
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| 75 | </p>
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| 76 |
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| 77 |
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| 78 | <!-- ####################################################### -->
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| 79 |
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| 80 | <hr />
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| 81 | <p class="fineprint"><em>
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| 82 | See <a href="17_intro/license.html">license.html</a> for copying conditions.
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| 83 | Comments and suggestions are welcome, and may be sent to
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| 84 | <a href="mailto:[email protected]">the libstdc++ mailing list</a>.
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| 85 | </em></p>
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| 86 |
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| 87 |
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| 88 | </body>
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| 89 | </html>
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