1<html lang="en"> 2<head> 3<title>Misnesting - The C Preprocessor</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="The C Preprocessor"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="Macro-Pitfalls.html#Macro-Pitfalls" title="Macro Pitfalls"> 9<link rel="next" href="Operator-Precedence-Problems.html#Operator-Precedence-Problems" title="Operator Precedence Problems"> 10<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 11<!-- 12Copyright (C) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 131997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 142008, 2009, 2010, 2011 15Free Software Foundation, Inc. 16 17Permission is granted to copy, distribute and/or modify this document 18under the terms of the GNU Free Documentation License, Version 1.3 or 19any later version published by the Free Software Foundation. A copy of 20the license is included in the 21section entitled ``GNU Free Documentation License''. 22 23This manual contains no Invariant Sections. The Front-Cover Texts are 24(a) (see below), and the Back-Cover Texts are (b) (see below). 25 26(a) The FSF's Front-Cover Text is: 27 28 A GNU Manual 29 30(b) The FSF's Back-Cover Text is: 31 32 You have freedom to copy and modify this GNU Manual, like GNU 33 software. Copies published by the Free Software Foundation raise 34 funds for GNU development. 35--> 36<meta http-equiv="Content-Style-Type" content="text/css"> 37<style type="text/css"><!-- 38 pre.display { font-family:inherit } 39 pre.format { font-family:inherit } 40 pre.smalldisplay { font-family:inherit; font-size:smaller } 41 pre.smallformat { font-family:inherit; font-size:smaller } 42 pre.smallexample { font-size:smaller } 43 pre.smalllisp { font-size:smaller } 44 span.sc { font-variant:small-caps } 45 span.roman { font-family:serif; font-weight:normal; } 46 span.sansserif { font-family:sans-serif; font-weight:normal; } 47--></style> 48<link rel="stylesheet" type="text/css" href="../cs.css"> 49</head> 50<body> 51<div class="node"> 52<a name="Misnesting"></a> 53<p> 54Next: <a rel="next" accesskey="n" href="Operator-Precedence-Problems.html#Operator-Precedence-Problems">Operator Precedence Problems</a>, 55Up: <a rel="up" accesskey="u" href="Macro-Pitfalls.html#Macro-Pitfalls">Macro Pitfalls</a> 56<hr> 57</div> 58 59<h4 class="subsection">3.10.1 Misnesting</h4> 60 61<p>When a macro is called with arguments, the arguments are substituted 62into the macro body and the result is checked, together with the rest of 63the input file, for more macro calls. It is possible to piece together 64a macro call coming partially from the macro body and partially from the 65arguments. For example, 66 67<pre class="smallexample"> #define twice(x) (2*(x)) 68 #define call_with_1(x) x(1) 69 call_with_1 (twice) 70 ==> twice(1) 71 ==> (2*(1)) 72</pre> 73 <p>Macro definitions do not have to have balanced parentheses. By writing 74an unbalanced open parenthesis in a macro body, it is possible to create 75a macro call that begins inside the macro body but ends outside of it. 76For example, 77 78<pre class="smallexample"> #define strange(file) fprintf (file, "%s %d", 79 ... 80 strange(stderr) p, 35) 81 ==> fprintf (stderr, "%s %d", p, 35) 82</pre> 83 <p>The ability to piece together a macro call can be useful, but the use of 84unbalanced open parentheses in a macro body is just confusing, and 85should be avoided. 86 87 </body></html> 88 89