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<title>C Plus Plus Expressions (Debugging with GDB)</title>

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<a name="C-Plus-Plus-Expressions"></a>
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<p>
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<hr>
<a name="C_002b_002b-Expressions"></a>
<h4 class="subsubsection">15.4.1.3 C<tt>++</tt> Expressions</h4>

<a name="index-expressions-in-C_002b_002b"></a>
<p><small>GDB</small> expression handling can interpret most C<tt>++</tt> expressions.
</p>
<a name="index-debugging-C_002b_002b-programs"></a>
<a name="index-C_002b_002b-compilers"></a>
<a name="index-debug-formats-and-C_002b_002b"></a>
<a name="index-GCC-and-C_002b_002b"></a>
<blockquote>
<p><em>Warning:</em> <small>GDB</small> can only debug C<tt>++</tt> code if you use
the proper compiler and the proper debug format.  Currently,
<small>GDB</small> works best when debugging C<tt>++</tt> code that is compiled
with the most recent version of <small>GCC</small> possible.  The DWARF
debugging format is preferred; <small>GCC</small> defaults to this on most
popular platforms.  Other compilers and/or debug formats are likely to
work badly or not at all when using <small>GDB</small> to debug C<tt>++</tt>
code.  See <a href="Compilation.html#Compilation">Compilation</a>.
</p></blockquote>

<ol>
<li> <a name="index-member-functions"></a>
Member function calls are allowed; you can use expressions like

<div class="smallexample">
<pre class="smallexample">count = aml-&gt;GetOriginal(x, y)
</pre></div>

</li><li> <a name="index-this_002c-inside-C_002b_002b-member-functions"></a>
<a name="index-namespace-in-C_002b_002b"></a>
While a member function is active (in the selected stack frame), your
expressions have the same namespace available as the member function;
that is, <small>GDB</small> allows implicit references to the class instance
pointer <code>this</code> following the same rules as C<tt>++</tt>.  <code>using</code>
declarations in the current scope are also respected by <small>GDB</small>.

</li><li> <a name="index-call-overloaded-functions"></a>
<a name="index-overloaded-functions_002c-calling"></a>
<a name="index-type-conversions-in-C_002b_002b"></a>
You can call overloaded functions; <small>GDB</small> resolves the function
call to the right definition, with some restrictions.  <small>GDB</small> does not
perform overload resolution involving user-defined type conversions,
calls to constructors, or instantiations of templates that do not exist
in the program.  It also cannot handle ellipsis argument lists or
default arguments.

<p>It does perform integral conversions and promotions, floating-point
promotions, arithmetic conversions, pointer conversions, conversions of
class objects to base classes, and standard conversions such as those of
functions or arrays to pointers; it requires an exact match on the
number of function arguments.
</p>
<p>Overload resolution is always performed, unless you have specified
<code>set overload-resolution off</code>.  See <a href="Debugging-C-Plus-Plus.html#Debugging-C-Plus-Plus"><small>GDB</small> Features for C<tt>++</tt></a>.
</p>
<p>You must specify <code>set overload-resolution off</code> in order to use an
explicit function signature to call an overloaded function, as in
</p><div class="smallexample">
<pre class="smallexample">p 'foo(char,int)'('x', 13)
</pre></div>

<p>The <small>GDB</small> command-completion facility can simplify this;
see <a href="Completion.html#Completion">Command Completion</a>.
</p>
</li><li> <a name="index-reference-declarations"></a>
<small>GDB</small> understands variables declared as C<tt>++</tt> lvalue or rvalue
references; you can use them in expressions just as you do in C<tt>++</tt>
source&mdash;they are automatically dereferenced.

<p>In the parameter list shown when <small>GDB</small> displays a frame, the values of
reference variables are not displayed (unlike other variables); this
avoids clutter, since references are often used for large structures.
The <em>address</em> of a reference variable is always shown, unless
you have specified &lsquo;<samp>set print address off</samp>&rsquo;.
</p>
</li><li> <small>GDB</small> supports the C<tt>++</tt> name resolution operator <code>::</code>&mdash;your
expressions can use it just as expressions in your program do.  Since
one scope may be defined in another, you can use <code>::</code> repeatedly if
necessary, for example in an expression like
&lsquo;<samp><var>scope1</var>::<var>scope2</var>::<var>name</var></samp>&rsquo;.  <small>GDB</small> also allows
resolving name scope by reference to source files, in both C and C<tt>++</tt>
debugging (see <a href="Variables.html#Variables">Program Variables</a>).

</li><li> <small>GDB</small> performs argument-dependent lookup, following the C<tt>++</tt>
specification.
</li></ol>

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