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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Interacting with C</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content=" ISO C++ , library "/><meta name="keywords" content=" ISO C++ , runtime , library "/><link rel="home" href="../index.html" title="The GNU C++ Library"/><link rel="up" href="numerics.html" title="Chapter 12. Numerics"/><link rel="prev" href="generalized_numeric_operations.html" title="Generalized Operations"/><link rel="next" href="io.html" title="Chapter 13. Input and Output"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Interacting with C</th></tr><tr><td align="left"><a accesskey="p" href="generalized_numeric_operations.html">Prev</a> </td><th width="60%" align="center">Chapter 12.
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Numerics
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</th><td align="right"> <a accesskey="n" href="io.html">Next</a></td></tr></table><hr/></div><div class="section" title="Interacting with C"><div class="titlepage"><div><div><h2 class="title"><a id="std.numerics.c"/>Interacting with C</h2></div></div></div><div class="section" title="Numerics vs. Arrays"><div class="titlepage"><div><div><h3 class="title"><a id="numerics.c.array"/>Numerics vs. Arrays</h3></div></div></div><p>One of the major reasons why FORTRAN can chew through numbers so well
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is that it is defined to be free of pointer aliasing, an assumption
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that C89 is not allowed to make, and neither is C++98. C99 adds a new
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keyword, <code class="code">restrict</code>, to apply to individual pointers. The
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C++ solution is contained in the library rather than the language
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(although many vendors can be expected to add this to their compilers
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as an extension).
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</p><p>That library solution is a set of two classes, five template classes,
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and "a whole bunch" of functions. The classes are required
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to be free of pointer aliasing, so compilers can optimize the
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daylights out of them the same way that they have been for FORTRAN.
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They are collectively called <code class="code">valarray</code>, although strictly
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speaking this is only one of the five template classes, and they are
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designed to be familiar to people who have worked with the BLAS
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libraries before.
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</p></div><div class="section" title="C99"><div class="titlepage"><div><div><h3 class="title"><a id="numerics.c.c99"/>C99</h3></div></div></div><p>In addition to the other topics on this page, we'll note here some
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of the C99 features that appear in libstdc++.
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</p><p>The C99 features depend on the <code class="code">--enable-c99</code> configure flag.
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This flag is already on by default, but it can be disabled by the
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user. Also, the configuration machinery will disable it if the
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necessary support for C99 (e.g., header files) cannot be found.
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</p><p>As of GCC 3.0, C99 support includes classification functions
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such as <code class="code">isnormal</code>, <code class="code">isgreater</code>,
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<code class="code">isnan</code>, etc.
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The functions used for 'long long' support such as <code class="code">strtoll</code>
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are supported, as is the <code class="code">lldiv_t</code> typedef. Also supported
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are the wide character functions using 'long long', like
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<code class="code">wcstoll</code>.
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</p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="generalized_numeric_operations.html">Prev</a> </td><td align="center"><a accesskey="u" href="numerics.html">Up</a></td><td align="right"> <a accesskey="n" href="io.html">Next</a></td></tr><tr><td align="left" valign="top">Generalized Operations </td><td align="center"><a accesskey="h" href="../index.html">Home</a></td><td align="right" valign="top"> Chapter 13.
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Input and Output
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</td></tr></table></div></body></html>
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