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| 22 | <title>Misnesting (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="Macro-Pitfalls.html" rel="up" title="Macro Pitfalls">
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| 33 | <link href="Operator-Precedence-Problems.html" rel="next" title="Operator Precedence Problems">
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| 56 |
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| 57 | <body lang="en">
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| 58 | <span id="Misnesting"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Operator-Precedence-Problems.html" accesskey="n" rel="next">Operator Precedence Problems</a>, Up: <a href="Macro-Pitfalls.html" accesskey="u" rel="up">Macro Pitfalls</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="Misnesting-1"></span><h4 class="subsubsection">26.5.10.1 Misnesting</h4>
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| 64 |
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| 65 | <p>When a macro is called with arguments, the arguments are substituted
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| 66 | into the macro body and the result is checked, together with the rest of
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| 67 | the input file, for more macro calls. It is possible to piece together
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| 68 | a macro call coming partially from the macro body and partially from the
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| 69 | arguments. For example,
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| 70 | </p>
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| 71 | <div class="example">
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| 72 | <pre class="example">#define twice(x) (2*(x))
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| 73 | #define call_with_1(x) x(1)
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| 74 | call_with_1 (twice)
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| 75 | → twice(1)
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| 76 | → (2*(1))
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| 77 | </pre></div>
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| 78 |
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| 79 | <p>Macro definitions do not have to have balanced parentheses. By writing
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| 80 | an unbalanced open parenthesis in a macro body, it is possible to create
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| 81 | a macro call that begins inside the macro body but ends outside of it.
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| 82 | For example,
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| 83 | </p>
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| 84 | <div class="example">
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| 85 | <pre class="example">#define strange(file) fprintf (file, "%s %d",
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| 86 | /* <span class="roman">…</span> */
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| 87 | strange(stderr) p, 35)
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| 88 | → fprintf (stderr, "%s %d", p, 35)
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| 89 | </pre></div>
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| 90 |
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| 91 | <p>The ability to piece together a macro call can be useful, but the use of
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| 92 | unbalanced open parentheses in a macro body is just confusing, and
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| 93 | should be avoided.
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| 94 | </p>
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| 95 |
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| 96 |
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| 97 |
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| 98 | </body>
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| 99 | </html>
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