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| 22 | <title>Sequence Points (GNU C Language Manual)</title>
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| 57 | <body lang="en">
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| 58 | <span id="Sequence-Points"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Postincrement-and-Ordering.html" accesskey="n" rel="next">Postincrement and Ordering</a>, Previous: <a href="Associativity-and-Ordering.html" accesskey="p" rel="prev">Associativity 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="Sequence-Points-1"></span><h3 class="section">10.3 Sequence Points</h3>
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| 64 | <span id="index-sequence-points"></span>
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| 65 | <span id="index-full-expression"></span>
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| 66 |
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| 67 | <p>There are some points in the code where C makes limited guarantees
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| 68 | about the order of operations. These are called <em>sequence
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| 69 | points</em>. Here is where they occur:
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| 70 | </p>
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| 71 | <ul>
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| 72 | <li> At the end of a <em>full expression</em>; that is to say, an expression
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| 73 | that is not part of a larger expression. All side effects specified
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| 74 | by that expression are carried out before execution moves
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| 75 | on to subsequent code.
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| 76 |
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| 77 | </li><li> At the end of the first operand of certain operators: ‘<samp>,</samp>’,
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| 78 | ‘<samp>&&</samp>’, ‘<samp>||</samp>’, and ‘<samp>?:</samp>’. All side effects specified by
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| 79 | that expression are carried out before any execution of the
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| 80 | next operand.
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| 81 |
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| 82 | <p>The commas that separate arguments in a function call are <em>not</em>
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| 83 | comma operators, and they do not create sequence points. The rule
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| 84 | for function arguments and the rule for operands are different
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| 85 | (see <a href="Ordering-of-Operands.html">Ordering of Operands</a>).
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| 86 | </p>
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| 87 | </li><li> Just before calling a function. All side effects specified by the
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| 88 | argument expressions are carried out before calling the function.
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| 89 |
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| 90 | <p>If the function to be called is not constant—that is, if it is
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| 91 | computed by an expression—all side effects in that expression are
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| 92 | carried out before calling the function.
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| 93 | </p></li></ul>
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| 94 |
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| 95 | <p>The ordering imposed by a sequence point applies locally to a limited
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| 96 | range of code, as stated above in each case. For instance, the
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| 97 | ordering imposed by the comma operator does not apply to code outside
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| 98 | that comma operator. Thus, in this code,
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| 99 | </p>
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| 100 | <div class="example">
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| 101 | <pre class="example">(x = 5, foo (x)) + x * x
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| 102 | </pre></div>
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| 103 |
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| 104 | <p>the sequence point of the comma operator orders <code>x = 5</code> before
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| 105 | <code>foo (x)</code>, but <code>x * x</code> could be computed before or after
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| 106 | them.
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| 107 | </p>
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| 108 | <hr>
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| 109 | <div class="header">
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| 110 | <p>
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| 111 | Next: <a href="Postincrement-and-Ordering.html" accesskey="n" rel="next">Postincrement and Ordering</a>, Previous: <a href="Associativity-and-Ordering.html" accesskey="p" rel="prev">Associativity 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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