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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

  2. <html>

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  16. <head>

  17. <meta http-equiv="Content-Type" content="text/html; charset=utf-8">

  18. <title>Range Checking (Debugging with GDB)</title>

  19. 

  20. <meta name="description" content="Range Checking (Debugging with GDB)">

  21. <meta name="keywords" content="Range Checking (Debugging with GDB)">

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  27. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  28. <link href="Checks.html#Checks" rel="up" title="Checks">

  29. <link href="Supported-Languages.html#Supported-Languages" rel="next" title="Supported Languages">

  30. <link href="Type-Checking.html#Type-Checking" rel="prev" title="Type Checking">

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  61. 

  62. <body lang="en">

  63. <a name="Range-Checking"></a>

  64. <div class="header">

  65. <p>

  66. Previous: <a href="Type-Checking.html#Type-Checking" accesskey="p" rel="prev">Type Checking</a>, Up: <a href="Checks.html#Checks" accesskey="u" rel="up">Checks</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>

  67. </div>

  68. <hr>

  69. <a name="An-Overview-of-Range-Checking"></a>

  70. <h4 class="subsection">15.3.2 An Overview of Range Checking</h4>

  71. 

  72. <p>In some languages (such as Modula-2), it is an error to exceed the

  73. bounds of a type; this is enforced with run-time checks.  Such range

  74. checking is meant to ensure program correctness by making sure

  75. computations do not overflow, or indices on an array element access do

  76. not exceed the bounds of the array.

  77. </p>

  78. <p>For expressions you use in <small>GDB</small> commands, you can tell

  79. <small>GDB</small> to treat range errors in one of three ways: ignore them,

  80. always treat them as errors and abandon the expression, or issue

  81. warnings but evaluate the expression anyway.

  82. </p>

  83. <p>A range error can result from numerical overflow, from exceeding an

  84. array index bound, or when you type a constant that is not a member

  85. of any type.  Some languages, however, do not treat overflows as an

  86. error.  In many implementations of C, mathematical overflow causes the

  87. result to &ldquo;wrap around&rdquo; to lower values&mdash;for example, if <var>m</var> is

  88. the largest integer value, and <var>s</var> is the smallest, then

  89. </p>

  90. <div class="smallexample">

  91. <pre class="smallexample"><var>m</var> + 1 &rArr; <var>s</var>

  92. </pre></div>

  93. 

  94. <p>This, too, is specific to individual languages, and in some cases

  95. specific to individual compilers or machines.  See <a href="Supported-Languages.html#Supported-Languages">Supported Languages</a>, for further details on specific languages.

  96. </p>

  97. <p><small>GDB</small> provides some additional commands for controlling the range checker:

  98. </p>

  99. <a name="index-set-check-range"></a>

  100. <a name="index-show-check-range"></a>

  101. <dl compact="compact">

  102. <dt><code>set check range auto</code></dt>

  103. <dd><p>Set range checking on or off based on the current working language.

  104. See <a href="Supported-Languages.html#Supported-Languages">Supported Languages</a>, for the default settings for

  105. each language.

  106. </p>

  107. </dd>

  108. <dt><code>set check range on</code></dt>

  109. <dt><code>set check range off</code></dt>

  110. <dd><p>Set range checking on or off, overriding the default setting for the

  111. current working language.  A warning is issued if the setting does not

  112. match the language default.  If a range error occurs and range checking is on,

  113. then a message is printed and evaluation of the expression is aborted.

  114. </p>

  115. </dd>

  116. <dt><code>set check range warn</code></dt>

  117. <dd><p>Output messages when the <small>GDB</small> range checker detects a range error,

  118. but attempt to evaluate the expression anyway.  Evaluating the

  119. expression may still be impossible for other reasons, such as accessing

  120. memory that the process does not own (a typical example from many Unix

  121. systems).

  122. </p>

  123. </dd>

  124. <dt><code>show range</code></dt>

  125. <dd><p>Show the current setting of the range checker, and whether or not it is

  126. being set automatically by <small>GDB</small>.

  127. </p></dd>

  128. </dl>

  129. 

  130. <hr>

  131. <div class="header">

  132. <p>

  133. Previous: <a href="Type-Checking.html#Type-Checking" accesskey="p" rel="prev">Type Checking</a>, Up: <a href="Checks.html#Checks" accesskey="u" rel="up">Checks</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>

  134. </div>

  135. 

  136. 

  137. 

  138. </body>

  139. </html>