| <html lang="en"> |
| <head> |
| <title>GNU C Variable-Size Arrays - The GNU C Library</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The GNU C Library"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Variable-Size-Automatic.html#Variable-Size-Automatic" title="Variable Size Automatic"> |
| <link rel="prev" href="Disadvantages-of-Alloca.html#Disadvantages-of-Alloca" title="Disadvantages of Alloca"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU C library. |
| |
| This is Edition 0.12, last updated 2007-10-27, |
| of `The GNU C Library Reference Manual', for version |
| 2.8 (Sourcery G++ Lite 2011.03-41). |
| |
| Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, |
| 2003, 2007, 2008, 2010 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software Needs Free Documentation'' |
| and ``GNU Lesser General Public License'', the Front-Cover texts being |
| ``A GNU Manual'', and with the Back-Cover Texts as in (a) below. A |
| copy of the license is included in the section entitled "GNU Free |
| Documentation License". |
| |
| (a) The FSF's Back-Cover Text is: ``You have the freedom to |
| copy and modify this GNU manual. Buying copies from the FSF |
| supports it in developing GNU and promoting software freedom.''--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="GNU-C-Variable-Size-Arrays"></a> |
| <a name="GNU-C-Variable_002dSize-Arrays"></a> |
| <p> |
| Previous: <a rel="previous" accesskey="p" href="Disadvantages-of-Alloca.html#Disadvantages-of-Alloca">Disadvantages of Alloca</a>, |
| Up: <a rel="up" accesskey="u" href="Variable-Size-Automatic.html#Variable-Size-Automatic">Variable Size Automatic</a> |
| <hr> |
| </div> |
| |
| <h5 class="subsubsection">3.2.5.4 GNU C Variable-Size Arrays</h5> |
| |
| <p><a name="index-variable_002dsized-arrays-349"></a> |
| In GNU C, you can replace most uses of <code>alloca</code> with an array of |
| variable size. Here is how <code>open2</code> would look then: |
| |
| <pre class="smallexample"> int open2 (char *str1, char *str2, int flags, int mode) |
| { |
| char name[strlen (str1) + strlen (str2) + 1]; |
| stpcpy (stpcpy (name, str1), str2); |
| return open (name, flags, mode); |
| } |
| </pre> |
| <p>But <code>alloca</code> is not always equivalent to a variable-sized array, for |
| several reasons: |
| |
| <ul> |
| <li>A variable size array's space is freed at the end of the scope of the |
| name of the array. The space allocated with <code>alloca</code> |
| remains until the end of the function. |
| |
| <li>It is possible to use <code>alloca</code> within a loop, allocating an |
| additional block on each iteration. This is impossible with |
| variable-sized arrays. |
| </ul> |
| |
| <p><strong>NB:</strong> If you mix use of <code>alloca</code> and variable-sized arrays |
| within one function, exiting a scope in which a variable-sized array was |
| declared frees all blocks allocated with <code>alloca</code> during the |
| execution of that scope. |
| |
| </body></html> |
| |
