mingw/info/gdb/Expressions.html

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  18 <h3 class="section">Expressions</h3>
  19
  20    <p><code>print</code> and many other GDB commands accept an expression and
  21 compute its value.  Any kind of constant, variable or operator defined
  22 by the programming language you are using is valid in an expression in
  23 GDB.  This includes conditional expressions, function calls, casts
  24 and string constants.  It unfortunately does not include symbols defined
  25 by preprocessor <code>#define</code> commands.
  26
  27    GDB supports array constants in expressions input by
  28 the user.  The syntax is {<var>element</var>, <var>element</var><small class="dots">...</small>}.  For example,
  29 you can use the command <code>print {1, 2, 3}</code> to build up an array in
  30 memory that is <code>malloc</code>ed in the target program.
  31
  32    <p>Because C is so widespread, most of the expressions shown in examples in
  33 this manual are in C.  See <a href="Languages.html#Languages">Using GDB with Different Languages</a>, for information on how to use expressions in other
  34 languages.
  35
  36    <p>In this section, we discuss operators that you can use in GDB
  37 expressions regardless of your programming language.
  38
  39    <p>Casts are supported in all languages, not just in C, because it is so
  40 useful to cast a number into a pointer in order to examine a structure
  41 at that address in memory.
  42
  43    GDB supports these operators, in addition to those common
  44 to programming languages:
  45
  46      <dl>
  47 <dt><code>@</code>
  48      <dd><code>@</code> is a binary operator for treating parts of memory as arrays.
  49 See <a href="Arrays.html#Arrays">Artificial arrays</a>, for more information.
  50
  51      <br><dt><code>::</code>
  52      <dd><code>::</code> allows you to specify a variable in terms of the file or
  53 function where it is defined.  See <a href="Variables.html#Variables">Program variables</a>.
  54
  55      <br><dt><code>{</code><var>type</var><code>} </code><var>addr</var><code></code>
  56      <dd>Refers to an object of type <var>type</var> stored at address <var>addr</var> in
  57 memory.  <var>addr</var> may be any expression whose value is an integer or
  58 pointer (but parentheses are required around binary operators, just as in
  59 a cast).  This construct is allowed regardless of what kind of data is
  60 normally supposed to reside at <var>addr</var>.
  61 </dl>
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