mingw/info/gdb/Range-Checking.html

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  12 Node:<a name="Range%20Checking">Range Checking</a>,
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  17
  18 <h4 class="subsection">An overview of range checking</h4>
  19
  20    <p>In some languages (such as Modula-2), it is an error to exceed the
  21 bounds of a type; this is enforced with run-time checks.  Such range
  22 checking is meant to ensure program correctness by making sure
  23 computations do not overflow, or indices on an array element access do
  24 not exceed the bounds of the array.
  25
  26    <p>For expressions you use in GDB commands, you can tell
  27 GDB to treat range errors in one of three ways: ignore them,
  28 always treat them as errors and abandon the expression, or issue
  29 warnings but evaluate the expression anyway.
  30
  31    <p>A range error can result from numerical overflow, from exceeding an
  32 array index bound, or when you type a constant that is not a member
  33 of any type.  Some languages, however, do not treat overflows as an
  34 error.  In many implementations of C, mathematical overflow causes the
  35 result to "wrap around" to lower values--for example, if <var>m</var> is
  36 the largest integer value, and <var>s</var> is the smallest, then
  37
  38 <pre class="example">     <var>m</var> + 1 =&gt; <var>s</var>
  39      </pre>
  40
  41    <p>This, too, is specific to individual languages, and in some cases
  42 specific to individual compilers or machines.  See <a href="Support.html#Support">Supported languages</a>, for further details on specific languages.
  43
  44    GDB provides some additional commands for controlling the range checker:
  45
  46      <dl>
  47 <dt><code>set check range auto</code>
  48      <dd>Set range checking on or off based on the current working language.
  49 See <a href="Support.html#Support">Supported languages</a>, for the default settings for
  50 each language.
  51
  52      <br><dt><code>set check range on</code>
  53      <dd><dt><code>set check range off</code>
  54      <dd>Set range checking on or off, overriding the default setting for the
  55 current working language.  A warning is issued if the setting does not
  56 match the language default.  If a range error occurs and range checking is on,
  57 then a message is printed and evaluation of the expression is aborted.
  58
  59      <br><dt><code>set check range warn</code>
  60      <dd>Output messages when the GDB range checker detects a range error,
  61 but attempt to evaluate the expression anyway.  Evaluating the
  62 expression may still be impossible for other reasons, such as accessing
  63 memory that the process does not own (a typical example from many Unix
  64 systems).
  65
  66      <br><dt><code>show range</code>
  67      <dd>Show the current setting of the range checker, and whether or not it is
  68 being set automatically by GDB.
  69 </dl>
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