| <html lang="en"> |
| <head> |
| <title>Range Checking - Debugging with GDB</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="Debugging with GDB"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Checks.html#Checks" title="Checks"> |
| <link rel="prev" href="Type-Checking.html#Type-Checking" title="Type Checking"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, |
| 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 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'' and ``Free Software Needs |
| Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,'' |
| and with the Back-Cover Texts as in (a) below. |
| |
| (a) The FSF's Back-Cover Text is: ``You are free to copy and modify |
| this GNU Manual. Buying copies from GNU Press supports the FSF 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="Range-Checking"></a> |
| <p> |
| Previous: <a rel="previous" accesskey="p" href="Type-Checking.html#Type-Checking">Type Checking</a>, |
| Up: <a rel="up" accesskey="u" href="Checks.html#Checks">Checks</a> |
| <hr> |
| </div> |
| |
| <h4 class="subsection">15.3.2 An Overview of Range Checking</h4> |
| |
| <p>In some languages (such as Modula-2), it is an error to exceed the |
| bounds of a type; this is enforced with run-time checks. Such range |
| checking is meant to ensure program correctness by making sure |
| computations do not overflow, or indices on an array element access do |
| not exceed the bounds of the array. |
| |
| <p>For expressions you use in <span class="sc">gdb</span> commands, you can tell |
| <span class="sc">gdb</span> to treat range errors in one of three ways: ignore them, |
| always treat them as errors and abandon the expression, or issue |
| warnings but evaluate the expression anyway. |
| |
| <p>A range error can result from numerical overflow, from exceeding an |
| array index bound, or when you type a constant that is not a member |
| of any type. Some languages, however, do not treat overflows as an |
| error. In many implementations of C, mathematical overflow causes the |
| result to “wrap around” to lower values—for example, if <var>m</var> is |
| the largest integer value, and <var>s</var> is the smallest, then |
| |
| <pre class="smallexample"> <var>m</var> + 1 ⇒ <var>s</var> |
| </pre> |
| <p>This, too, is specific to individual languages, and in some cases |
| specific to individual compilers or machines. See <a href="Supported-Languages.html#Supported-Languages">Supported Languages</a>, for further details on specific languages. |
| |
| <p><span class="sc">gdb</span> provides some additional commands for controlling the range checker: |
| |
| <p><a name="index-set-check-range-791"></a><a name="index-show-check-range-792"></a> |
| <dl> |
| <dt><code>set check range auto</code><dd>Set range checking on or off based on the current working language. |
| See <a href="Supported-Languages.html#Supported-Languages">Supported Languages</a>, for the default settings for |
| each language. |
| |
| <br><dt><code>set check range on</code><dt><code>set check range off</code><dd>Set range checking on or off, overriding the default setting for the |
| current working language. A warning is issued if the setting does not |
| match the language default. If a range error occurs and range checking is on, |
| then a message is printed and evaluation of the expression is aborted. |
| |
| <br><dt><code>set check range warn</code><dd>Output messages when the <span class="sc">gdb</span> range checker detects a range error, |
| but attempt to evaluate the expression anyway. Evaluating the |
| expression may still be impossible for other reasons, such as accessing |
| memory that the process does not own (a typical example from many Unix |
| systems). |
| |
| <br><dt><code>show range</code><dd>Show the current setting of the range checker, and whether or not it is |
| being set automatically by <span class="sc">gdb</span>. |
| </dl> |
| |
| </body></html> |
| |
