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| 22 | <title>Explicit Type Conversion (GNU C Language Manual)</title>
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| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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| 32 | <link href="Type-Conversions.html" rel="up" title="Type Conversions">
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| 33 | <link href="Assignment-Type-Conversions.html" rel="next" title="Assignment Type Conversions">
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| 57 | <body lang="en">
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| 58 | <span id="Explicit-Type-Conversion"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Assignment-Type-Conversions.html" accesskey="n" rel="next">Assignment Type Conversions</a>, Up: <a href="Type-Conversions.html" accesskey="u" rel="up">Type Conversions</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="Explicit-Type-Conversion-1"></span><h3 class="section">24.1 Explicit Type Conversion</h3>
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| 64 | <span id="index-cast"></span>
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| 65 | <span id="index-explicit-type-conversion"></span>
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| 66 |
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| 67 | <p>You can do explicit conversions using the unary <em>cast</em> operator,
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| 68 | which is written as a type designator (see <a href="Type-Designators.html">Type Designators</a>) in
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| 69 | parentheses. For example, <code>(int)</code> is the operator to cast to
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| 70 | type <code>int</code>. Here’s an example of using it:
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| 71 | </p>
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| 72 | <div class="example">
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| 73 | <pre class="example">{
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| 74 | double d = 5.5;
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| 75 |
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| 76 | printf ("Floating point value: %f\n", d);
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| 77 | printf ("Rounded to integer: %d\n", (int) d);
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| 78 | }
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| 79 | </pre></div>
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| 80 |
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| 81 | <p>Using <code>(int) d</code> passes an <code>int</code> value as argument to
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| 82 | <code>printf</code>, so you can print it with ‘<samp>%d</samp>’. Using just
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| 83 | <code>d</code> without the cast would pass the value as <code>double</code>.
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| 84 | That won’t work at all with ‘<samp>%d</samp>’; the results would be gibberish.
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| 85 | </p>
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| 86 | <p>To divide one integer by another without rounding,
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| 87 | cast either of the integers to <code>double</code> first:
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| 88 | </p>
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| 89 | <div class="example">
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| 90 | <pre class="example">(double) <var>dividend</var> / <var>divisor</var>
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| 91 | <var>dividend</var> / (double) <var>divisor</var>
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| 92 | </pre></div>
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| 93 |
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| 94 | <p>It is enough to cast one of them, because that forces the common type
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| 95 | to <code>double</code> so the other will be converted automatically.
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| 96 | </p>
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| 97 | <p>The valid cast conversions are:
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| 98 | </p>
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| 99 | <ul>
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| 100 | <li> One numerical type to another.
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| 101 |
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| 102 | </li><li> One pointer type to another.
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| 103 | (Converting between pointers that point to functions
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| 104 | and pointers that point to data is not standard C.)
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| 105 |
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| 106 | </li><li> A pointer type to an integer type.
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| 107 |
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| 108 | </li><li> An integer type to a pointer type.
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| 109 |
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| 110 | </li><li> To a union type, from the type of any alternative in the union
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| 111 | (see <a href="Unions.html">Unions</a>). (This is a GNU extension.)
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| 112 |
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| 113 | </li><li> Anything, to <code>void</code>.
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| 114 | </li></ul>
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| 115 |
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| 116 |
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| 117 |
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| 118 |
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