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82 lines
3.6 KiB
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82 lines
3.6 KiB
HTML
4 years ago
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<title>Conditionals - 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 rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions">
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<link rel="prev" href="Typeof.html#Typeof" title="Typeof">
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<link rel="next" href="_005f_005fint128.html#g_t_005f_005fint128" title="__int128">
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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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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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<div class="node">
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<a name="Conditionals"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="_005f_005fint128.html#g_t_005f_005fint128">__int128</a>,
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Previous: <a rel="previous" accesskey="p" href="Typeof.html#Typeof">Typeof</a>,
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Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a>
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<hr>
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</div>
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<h3 class="section">6.7 Conditionals with Omitted Operands</h3>
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<p><a name="index-conditional-expressions_002c-extensions-2897"></a><a name="index-omitted-middle_002doperands-2898"></a><a name="index-middle_002doperands_002c-omitted-2899"></a><a name="index-extensions_002c-_0040code_007b_003f_003a_007d-2900"></a><a name="index-g_t_0040code_007b_003f_003a_007d-extensions-2901"></a>
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The middle operand in a conditional expression may be omitted. Then
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if the first operand is nonzero, its value is the value of the conditional
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expression.
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<p>Therefore, the expression
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<pre class="smallexample"> x ? : y
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</pre>
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<p class="noindent">has the value of <code>x</code> if that is nonzero; otherwise, the value of
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<code>y</code>.
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<p>This example is perfectly equivalent to
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<pre class="smallexample"> x ? x : y
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</pre>
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<p><a name="index-side-effect-in-_0040code_007b_003f_003a_007d-2902"></a><a name="index-g_t_0040code_007b_003f_003a_007d-side-effect-2903"></a>In this simple case, the ability to omit the middle operand is not
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especially useful. When it becomes useful is when the first operand does,
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or may (if it is a macro argument), contain a side effect. Then repeating
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the operand in the middle would perform the side effect twice. Omitting
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the middle operand uses the value already computed without the undesirable
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effects of recomputing it.
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