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100 lines
4.4 KiB
HTML
100 lines
4.4 KiB
HTML
4 years ago
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<html lang="en">
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<title>Arrays and pointers implementation - Using the GNU Compiler Collection (GCC)</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="C-Implementation.html#C-Implementation" title="C Implementation">
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<link rel="prev" href="Floating-point-implementation.html#Floating-point-implementation" title="Floating point implementation">
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<link rel="next" href="Hints-implementation.html#Hints-implementation" title="Hints implementation">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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</head>
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<body>
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<div class="node">
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<a name="Arrays-and-pointers-implementation"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Hints-implementation.html#Hints-implementation">Hints implementation</a>,
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Previous: <a rel="previous" accesskey="p" href="Floating-point-implementation.html#Floating-point-implementation">Floating point implementation</a>,
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Up: <a rel="up" accesskey="u" href="C-Implementation.html#C-Implementation">C Implementation</a>
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<hr>
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</div>
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<h3 class="section">4.7 Arrays and Pointers</h3>
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<ul>
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<li><cite>The result of converting a pointer to an integer or
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vice versa (C90 6.3.4, C99 and C11 6.3.2.3).</cite>
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<p>A cast from pointer to integer discards most-significant bits if the
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pointer representation is larger than the integer type,
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sign-extends<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a>
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if the pointer representation is smaller than the integer type, otherwise
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the bits are unchanged.
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<!-- ??? We've always claimed that pointers were unsigned entities. -->
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<!-- Shouldn't we therefore be doing zero-extension? If so, the bug -->
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<!-- is in convert_to_integer, where we call type_for_size and request -->
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<!-- a signed integral type. On the other hand, it might be most useful -->
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<!-- for the target if we extend according to POINTERS_EXTEND_UNSIGNED. -->
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<p>A cast from integer to pointer discards most-significant bits if the
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pointer representation is smaller than the integer type, extends according
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to the signedness of the integer type if the pointer representation
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is larger than the integer type, otherwise the bits are unchanged.
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<p>When casting from pointer to integer and back again, the resulting
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pointer must reference the same object as the original pointer, otherwise
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the behavior is undefined. That is, one may not use integer arithmetic to
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avoid the undefined behavior of pointer arithmetic as proscribed in
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C99 and C11 6.5.6/8.
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<li><cite>The size of the result of subtracting two pointers to elements
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of the same array (C90 6.3.6, C99 and C11 6.5.6).</cite>
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<p>The value is as specified in the standard and the type is determined
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by the ABI.
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</ul>
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<div class="footnote">
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<hr>
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<h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> Future versions of GCC may zero-extend, or use
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a target-defined <code>ptr_extend</code> pattern. Do not rely on sign extension.</p>
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<hr></div>
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</body></html>
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