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<h3 class="section">10.1 Expressions</h3>

<p><a name="index-expressions-494"></a><code>print</code> and many other <span class="sc">gdb</span> commands accept an expression and
compute its value.  Any kind of constant, variable or operator defined
by the programming language you are using is valid in an expression in
<span class="sc">gdb</span>.  This includes conditional expressions, function calls,
casts, and string constants.  It also includes preprocessor macros, if
you compiled your program to include this information; see
<a href="Compilation.html#Compilation">Compilation</a>.

   <p><a name="index-arrays-in-expressions-495"></a><span class="sc">gdb</span> supports array constants in expressions input by
the user.  The syntax is {<var>element</var>, <var>element</var><small class="dots">...</small>}.  For example,
you can use the command <code>print {1, 2, 3}</code> to create an array
of three integers.  If you pass an array to a function or assign it
to a program variable, <span class="sc">gdb</span> copies the array to memory that
is <code>malloc</code>ed in the target program.

   <p>Because C is so widespread, most of the expressions shown in examples in
this manual are in C.  See <a href="Languages.html#Languages">Using <span class="sc">gdb</span> with Different Languages</a>, for information on how to use expressions in other
languages.

   <p>In this section, we discuss operators that you can use in <span class="sc">gdb</span>
expressions regardless of your programming language.

   <p><a name="index-casts_002c-in-expressions-496"></a>Casts are supported in all languages, not just in C, because it is so
useful to cast a number into a pointer in order to examine a structure
at that address in memory. 
<!-- FIXME: casts supported-Mod2 true? -->

   <p><span class="sc">gdb</span> supports these operators, in addition to those common
to programming languages:

     <dl>
<dt><code>@</code><dd>&lsquo;<samp><span class="samp">@</span></samp>&rsquo; is a binary operator for treating parts of memory as arrays. 
See <a href="Arrays.html#Arrays">Artificial Arrays</a>, for more information.

     <br><dt><code>::</code><dd>&lsquo;<samp><span class="samp">::</span></samp>&rsquo; allows you to specify a variable in terms of the file or
function where it is defined.  See <a href="Variables.html#Variables">Program Variables</a>.

     <p><a name="index-g_t_0040_007b_0040var_007btype_007d_0040_007d-497"></a><a name="index-type-casting-memory-498"></a><a name="index-memory_002c-viewing-as-typed-object-499"></a><a name="index-casts_002c-to-view-memory-500"></a><br><dt><code>{</code><var>type</var><code>} </code><var>addr</var><dd>Refers to an object of type <var>type</var> stored at address <var>addr</var> in
memory.  <var>addr</var> may be any expression whose value is an integer or
pointer (but parentheses are required around binary operators, just as in
a cast).  This construct is allowed regardless of what kind of data is
normally supposed to reside at <var>addr</var>. 
</dl>

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