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<title>Using the GNU Compiler Collection (GCC): Arrays and pointers implementation</title>
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<a name="Arrays-and-pointers-implementation"></a>
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<p>
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Next: <a href="Hints-implementation.html#Hints-implementation" accesskey="n" rel="next">Hints implementation</a>, Previous: <a href="Floating-point-implementation.html#Floating-point-implementation" accesskey="p" rel="prev">Floating point implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="Arrays-and-Pointers"></a>
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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 name="DOCF2" href="#FOOT2"><sup>2</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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</p>
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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>
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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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</p>
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</li><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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</p>
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</li></ul>
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<div class="footnote">
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<hr>
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<h4 class="footnotes-heading">Footnotes</h4>
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<h3><a name="FOOT2" href="#DOCF2">(2)</a></h3>
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<p>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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