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| 32 | <link href="Order-of-Execution.html" rel="up" title="Order of Execution">
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| 33 | <link href="Optimization-and-Ordering.html" rel="next" title="Optimization and Ordering">
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| 58 | <span id="Ordering-of-Operands"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Optimization-and-Ordering.html" accesskey="n" rel="next">Optimization and Ordering</a>, Previous: <a href="Postincrement-and-Ordering.html" accesskey="p" rel="prev">Postincrement and Ordering</a>, Up: <a href="Order-of-Execution.html" accesskey="u" rel="up">Order of Execution</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="Ordering-of-Operands-1"></span><h3 class="section">10.5 Ordering of Operands</h3>
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| 64 | <span id="index-ordering-of-operands-1"></span>
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| 65 | <span id="index-operand-ordering"></span>
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| 66 |
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| 67 | <p>Operands and arguments can be computed in any order, but there are limits to
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| 68 | this intermixing in GNU C:
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| 69 | </p>
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| 70 | <ul>
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| 71 | <li> The operands of a binary arithmetic operator can be computed in either
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| 72 | order, but they can’t be intermixed: one of them has to come first,
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| 73 | followed by the other. Any side effects in the operand that’s computed
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| 74 | first are executed before the other operand is computed.
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| 75 |
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| 76 | </li><li> That applies to assignment operators too, except that in simple assignment
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| 77 | the previous value of the left operand is unused.
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| 78 |
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| 79 | </li><li> The arguments in a function call can be computed in any order, but
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| 80 | they can’t be intermixed. Thus, one argument is fully computed, then
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| 81 | another, and so on until they are all done. Any side effects in one argument
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| 82 | are executed before computation of another argument begins.
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| 83 | </li></ul>
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| 84 |
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| 85 | <p>These rules don’t cover side effects caused by postincrement and
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| 86 | postdecrement operators—those can be deferred up to the next
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| 87 | sequence point.
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| 88 | </p>
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| 89 | <p>If you want to get pedantic, the fact is that GCC can reorder the
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| 90 | computations in many other ways provided that doesn’t alter the result
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| 91 | of running the program. However, because they don’t alter the result
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| 92 | of running the program, they are negligible, unless you are concerned
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| 93 | with the values in certain variables at various times as seen by other
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| 94 | processes. In those cases, you can use <code>volatile</code> to prevent
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| 95 | optimizations that would make them behave strangely. See <a href="volatile.html">volatile</a>.
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| 96 | </p>
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| 97 |
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| 99 |
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