mingw/info/gdb/Values-and-their-Operations.html

   1 <html lang="en">
   2 <head>
   3 <title>Debugging with GDB</title>
   4 <meta http-equiv="Content-Type" content="text/html">
   5 <meta name="description" content="Debugging with GDB">
   6 <meta name="generator" content="makeinfo 4.3">
   7 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home">
   8 </head>
   9 <body>
  10 <div class="node">
  11 <p>
  12 Node:<a name="Values%20and%20their%20Operations">Values and their Operations</a>,
  13 Next:<a rel="next" accesskey="n" href="Chill-type-and-range-checks.html#Chill%20type%20and%20range%20checks">Chill type and range checks</a>,
  14 Previous:<a rel="previous" accesskey="p" href="Locations.html#Locations">Locations</a>,
  15 Up:<a rel="up" accesskey="u" href="Chill.html#Chill">Chill</a>
  16 <hr><br>
  17 </div>
  18
  19 <h5 class="subsubsection">Values and their Operations</h5>
  20
  21    <p>Values are used to alter locations, to investigate complex structures in
  22 more detail or to filter relevant information out of a large amount of
  23 data.  There are several (mode dependent) operations defined which enable
  24 such investigations.  These operations are not only applicable to
  25 constant values but also to locations, which can become quite useful
  26 when debugging complex structures.  During parsing the command line
  27 (e.g. evaluating an expression) GDB treats location names as
  28 the values behind these locations.
  29
  30    <p>This section describes how values have to be specified and which
  31 operations are legal to be used with such values.
  32
  33      <dl>
  34 <dt><code>Literal Values</code>
  35      <dd>Literal values are specified in the same manner as in <small>GNU</small> Chill programs.
  36 For detailed specification refer to the <small>GNU</small> Chill implementation Manual
  37 chapter 1.5.
  38
  39      <br><dt><code>Tuple Values</code>
  40      <dd>A tuple is specified by <code>&lt;mode name&gt;[&lt;tuple&gt;]</code>, where <code>&lt;mode
  41 name&gt;</code> can be omitted if the mode of the tuple is unambiguous.  This
  42 unambiguity is derived from the context of a evaluated expression.
  43 <code>&lt;tuple&gt;</code> can be one of the following:
  44
  45           <ul>
  46 <li><em>Powerset Tuple</em>
  47 <li><em>Array Tuple</em>
  48 <li><em>Structure Tuple</em>
  49 Powerset tuples, array tuples and structure tuples are specified in the
  50 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
  51 </ul>
  52
  53      <br><dt><code>String Element Value</code>
  54      <dd>A string element value is specified by
  55      <pre class="smallexample">          <code>&lt;string value&gt;(&lt;index&gt;)</code>
  56           </pre>
  57      where <code>&lt;index&gt;</code> is a integer expression.  It delivers a character
  58 value which is equivalent to the character indexed by <code>&lt;index&gt;</code> in
  59 the string.
  60
  61      <br><dt><code>String Slice Value</code>
  62      <dd>A string slice value is specified by <code>&lt;string value&gt;(&lt;slice
  63 spec&gt;)</code>, where <code>&lt;slice spec&gt;</code> can be either a range of integer
  64 expressions or specified by <code>&lt;start expr&gt; up &lt;size&gt;</code>.
  65 <code>&lt;size&gt;</code> denotes the number of elements which the slice contains.
  66 The delivered value is a string value, which is part of the specified
  67 string.
  68
  69      <br><dt><code>Array Element Values</code>
  70      <dd>An array element value is specified by <code>&lt;array value&gt;(&lt;expr&gt;)</code> and
  71 delivers a array element value of the mode of the specified array.
  72
  73      <br><dt><code>Array Slice Values</code>
  74      <dd>An array slice is specified by <code>&lt;array value&gt;(&lt;slice spec&gt;)</code>, where
  75 <code>&lt;slice spec&gt;</code> can be either a range specified by expressions or by
  76 <code>&lt;start expr&gt; up &lt;size&gt;</code>.  <code>&lt;size&gt;</code> denotes the number of
  77 arrayelements the slice contains.  The delivered value is an array value
  78 which is part of the specified array.
  79
  80      <br><dt><code>Structure Field Values</code>
  81      <dd>A structure field value is derived by <code>&lt;structure value&gt;.&lt;field
  82 name&gt;</code>, where <code>&lt;field name&gt;</code> indicates the name of a field specified
  83 in the mode definition of the structure.  The mode of the delivered value
  84 corresponds to this mode definition in the structure definition.
  85
  86      <br><dt><code>Procedure Call Value</code>
  87      <dd>The procedure call value is derived from the return value of the
  88 procedure<a rel="footnote" href="#fn-1"><sup>1</sup></a>.
  89
  90      <p>Values of duration mode locations are represented by <code>ULONG</code> literals.
  91
  92      <p>Values of time mode locations appear as
  93      <pre class="smallexample">          <code>TIME(&lt;secs&gt;:&lt;nsecs&gt;)</code>
  94           </pre>
  95
  96      <br><dt><code>Zero-adic Operator Value</code>
  97      <dd>The zero-adic operator value is derived from the instance value for the
  98 current active process.
  99
 100      <br><dt><code>Expression Values</code>
 101      <dd>The value delivered by an expression is the result of the evaluation of
 102 the specified expression.  If there are error conditions (mode
 103 incompatibility, etc.) the evaluation of expressions is aborted with a
 104 corresponding error message.  Expressions may be parenthesised which
 105 causes the evaluation of this expression before any other expression
 106 which uses the result of the parenthesised expression.  The following
 107 operators are supported by GDB:
 108
 109           <dl>
 110 <dt><code>OR, ORIF, XOR</code>
 111           <dd><dt><code>AND, ANDIF</code>
 112           <dd><dt><code>NOT</code>
 113           <dd>Logical operators defined over operands of boolean mode.
 114
 115           <br><dt><code>=, /=</code>
 116           <dd>Equality and inequality operators defined over all modes.
 117
 118           <br><dt><code>&gt;, &gt;=</code>
 119           <dd><dt><code>&lt;, &lt;=</code>
 120           <dd>Relational operators defined over predefined modes.
 121
 122           <br><dt><code>+, -</code>
 123           <dd><dt><code>*, /, MOD, REM</code>
 124           <dd>Arithmetic operators defined over predefined modes.
 125
 126           <br><dt><code>-</code>
 127           <dd>Change sign operator.
 128
 129           <br><dt><code>//</code>
 130           <dd>String concatenation operator.
 131
 132           <br><dt><code>()</code>
 133           <dd>String repetition operator.
 134
 135           <br><dt><code>-&gt;</code>
 136           <dd>Referenced location operator which can be used either to take the
 137 address of a location (<code>-&gt;loc</code>), or to dereference a reference
 138 location (<code>loc-&gt;</code>).
 139
 140           <br><dt><code>OR, XOR</code>
 141           <dd><dt><code>AND</code>
 142           <dd><dt><code>NOT</code>
 143           <dd>Powerset and bitstring operators.
 144
 145           <br><dt><code>&gt;, &gt;=</code>
 146           <dd><dt><code>&lt;, &lt;=</code>
 147           <dd>Powerset inclusion operators.
 148
 149           <br><dt><code>IN</code>
 150           <dd>Membership operator.
 151 </dl>
 152 </dl>
 153
 154    <div class="footnote">
 155 <hr>
 156 <h4>Footnotes</h4>
 157 <ol type="1">
 158 <li><a name="fn-1"></a>
 159 <p>If a procedure call is used for instance in an
 160 expression, then this procedure is called with all its side
 161 effects.  This can lead to confusing results if used carelessly.</p>
 162
 163    </ol><hr></div>
 164
 165    </body></html>
 166