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| 22 | <title>Conditional Branches (GNU C Language Manual)</title>
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| 30 | <link href="Symbol-Index.html" rel="index" title="Symbol Index">
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| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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| 32 | <link href="Conditional-Expression.html" rel="up" title="Conditional Expression">
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| 33 | <link href="Comma-Operator.html" rel="next" title="Comma Operator">
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| 34 | <link href="Conditional-Rules.html" rel="prev" title="Conditional Rules">
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| 56 |
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| 57 | <body lang="en">
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| 58 | <span id="Conditional-Branches"></span><div class="header">
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| 59 | <p>
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| 60 | Previous: <a href="Conditional-Rules.html" accesskey="p" rel="prev">Conditional Rules</a>, Up: <a href="Conditional-Expression.html" accesskey="u" rel="up">Conditional Expression</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="Conditional-Operator-Branches"></span><h4 class="subsection">8.4.2 Conditional Operator Branches</h4>
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| 64 | <span id="index-branches-of-conditional-expression"></span>
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| 65 |
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| 66 | <p>We call <var>iftrue</var> and <var>iffalse</var> the <em>branches</em> of the
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| 67 | conditional.
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| 68 | </p>
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| 69 | <p>The two branches should normally have the same type, but a few
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| 70 | exceptions are allowed. If they are both numeric types, the
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| 71 | conditional converts both to their common type (see <a href="Common-Type.html">Common Type</a>).
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| 72 | </p>
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| 73 | <p>With pointers (see <a href="Pointers.html">Pointers</a>), the two values can be pointers to
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| 74 | nearly compatible types (see <a href="Compatible-Types.html">Compatible Types</a>). In this case, the
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| 75 | result type is a similar pointer whose target type combines all the
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| 76 | type qualifiers (see <a href="Type-Qualifiers.html">Type Qualifiers</a>) of both branches.
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| 77 | </p>
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| 78 | <p>If one branch has type <code>void *</code> and the other is a pointer to an
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| 79 | object (not to a function), the conditional converts the <code>void *</code>
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| 80 | branch to the type of the other.
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| 81 | </p>
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| 82 | <p>If one branch is an integer constant with value zero and the other is
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| 83 | a pointer, the conditional converts zero to the pointer’s type.
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| 84 | </p>
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| 85 | <p>In GNU C, you can omit <var>iftrue</var> in a conditional expression. In
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| 86 | that case, if <var>condition</var> is nonzero, its value becomes the value of
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| 87 | the conditional expression, after conversion to the common type.
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| 88 | Thus,
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| 89 | </p>
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| 90 | <div class="example">
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| 91 | <pre class="example">x ? : y
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| 92 | </pre></div>
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| 93 |
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| 94 | <p>has the value of <code>x</code> if that is nonzero; otherwise, the value of
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| 95 | <code>y</code>.
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| 96 | </p>
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| 97 | <span id="index-side-effect-in-_003f_003a"></span>
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| 98 | <span id="index-_003f_003a-side-effect"></span>
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| 99 | <p>Omitting <var>iftrue</var> is useful when <var>condition</var> has side effects.
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| 100 | In that case, writing that expression twice would carry out the side
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| 101 | effects twice, but writing it once does them just once. For example,
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| 102 | if we suppose that the function <code>next_element</code> advances a pointer
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| 103 | variable to point to the next element in a list and returns the new
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| 104 | pointer,
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| 105 | </p>
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| 106 | <div class="example">
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| 107 | <pre class="example">next_element () ? : default_pointer
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| 108 | </pre></div>
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| 109 |
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| 110 | <p>is a way to advance the pointer and use its new value if it isn’t
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| 111 | null, but use <code>default_pointer</code> if that is null. We must not do
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| 112 | it this way,
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| 113 | </p>
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| 114 | <div class="example">
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| 115 | <pre class="example">next_element () ? next_element () : default_pointer
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| 116 | </pre></div>
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| 117 |
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| 118 | <p>because it would advance the pointer a second time.
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| 119 | </p>
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| 120 | <hr>
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| 121 | <div class="header">
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| 122 | <p>
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| 123 | Previous: <a href="Conditional-Rules.html" accesskey="p" rel="prev">Conditional Rules</a>, Up: <a href="Conditional-Expression.html" accesskey="u" rel="up">Conditional Expression</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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| 124 | </div>
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| 125 |
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| 126 |
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| 127 |
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