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| 58 | <span id="Pointer_002dInteger-Conversion"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Printing-Pointers.html" accesskey="n" rel="next">Printing Pointers</a>, Previous: <a href="Pointer-Arithmetic-Drawbacks.html" accesskey="p" rel="prev">Pointer Arithmetic Drawbacks</a>, Up: <a href="Pointers.html" accesskey="u" rel="up">Pointers</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
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| 61 | </div>
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| 62 | <hr>
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| 63 | <span id="Pointer_002dInteger-Conversion-1"></span><h3 class="section">14.15 Pointer-Integer Conversion</h3>
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| 64 | <span id="index-pointer_002dinteger-conversion"></span>
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| 65 | <span id="index-conversion-between-pointers-and-integers"></span>
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| 66 | <span id="index-uintptr_005ft"></span>
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| 67 |
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| 68 | <p>On modern computers, an address is simply a number. It occupies the
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| 69 | same space as some size of integer. In C, you can convert a pointer
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| 70 | to the appropriate integer types and vice versa, without losing
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| 71 | information. The appropriate integer types are <code>uintptr_t</code> (an
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| 72 | unsigned type) and <code>intptr_t</code> (a signed type). Both are defined
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| 73 | in <samp>stdint.h</samp>.
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| 74 | </p>
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| 75 | <p>For instance,
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| 76 | </p>
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| 77 | <div class="example">
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| 78 | <pre class="example">#include <stdint.h>
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| 79 | #include <stdio.h>
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| 80 |
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| 81 | void
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| 82 | print_pointer (void *ptr)
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| 83 | {
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| 84 | uintptr_t converted = (uintptr_t) ptr;
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| 85 |
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| 86 | printf ("Pointer value is 0x%x\n",
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| 87 | (unsigned int) converted);
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| 88 | }
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| 89 | </pre></div>
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| 90 |
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| 91 | <p>The specification ‘<samp>%x</samp>’ in the template (the first argument) for
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| 92 | <code>printf</code> means to represent this argument using hexadecimal
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| 93 | notation. It’s cleaner to use <code>uintptr_t</code>, since hexadecimal
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| 94 | printing treats the number as unsigned, but it won’t actually matter:
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| 95 | all <code>printf</code> gets to see is the series of bits in the number.
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| 96 | </p>
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| 97 | <p><strong>Warning:</strong> Converting pointers to integers is risky—don’t do
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| 98 | it unless it is really necessary.
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| 99 | </p>
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| 100 |
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| 101 |
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| 102 |
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