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<h5 class="subsubsection">15.4.1.3 C<tt>++</tt> Expressions</h5>

<p><a name="index-expressions-in-C_0040t_007b_002b_002b_007d-988"></a><span class="sc">gdb</span> expression handling can interpret most C<tt>++</tt> expressions.

   <p><a name="index-debugging-C_0040t_007b_002b_002b_007d-programs-989"></a><a name="index-C_0040t_007b_002b_002b_007d-compilers-990"></a><a name="index-debug-formats-and-C_0040t_007b_002b_002b_007d-991"></a><a name="index-g_t_0040value_007bNGCC_007d-and-C_0040t_007b_002b_002b_007d-992"></a><blockquote>
<em>Warning:</em> <span class="sc">gdb</span> can only debug C<tt>++</tt> code if you use
the proper compiler and the proper debug format.  Currently,
<span class="sc">gdb</span> works best when debugging C<tt>++</tt> code that is compiled
with the most recent version of <span class="sc">gcc</span> possible.  The DWARF
debugging format is preferred; <span class="sc">gcc</span> defaults to this on most
popular platforms.  Other compilers and/or debug formats are likely to
work badly or not at all when using <span class="sc">gdb</span> to debug C<tt>++</tt>
code.  See <a href="Compilation.html#Compilation">Compilation</a>. 
</blockquote>

     <ol type=1 start=1>

     <p><a name="index-member-functions-993"></a><li>Member function calls are allowed; you can use expressions like

     <pre class="smallexample">          count = aml-&gt;GetOriginal(x, y)
</pre>
     <p><a name="index-this_0040r_007b_002c-inside-C_0040t_007b_002b_002b_007d-member-functions_007d-994"></a><a name="index-namespace-in-C_0040t_007b_002b_002b_007d-995"></a><li>While a member function is active (in the selected stack frame), your
expressions have the same namespace available as the member function;
that is, <span class="sc">gdb</span> 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 <span class="sc">gdb</span>.

     <p><a name="index-call-overloaded-functions-996"></a><a name="index-overloaded-functions_002c-calling-997"></a><a name="index-type-conversions-in-C_0040t_007b_002b_002b_007d-998"></a><li>You can call overloaded functions; <span class="sc">gdb</span> resolves the function
call to the right definition, with some restrictions.  <span class="sc">gdb</span> 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>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"><span class="sc">gdb</span> Features for C<tt>++</tt></a>.

     <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
     <pre class="smallexample">          p 'foo(char,int)'('x', 13)
</pre>
     <p>The <span class="sc">gdb</span> command-completion facility can simplify this;
see <a href="Completion.html#Completion">Command Completion</a>.

     <p><a name="index-reference-declarations-999"></a><li><span class="sc">gdb</span> 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 <span class="sc">gdb</span> 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><span class="samp">set print address off</span></samp>&rsquo;.

     <li><span class="sc">gdb</span> 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><span class="samp">::</span><var>scope2</var><span class="samp">::</span><var>name</var></samp>&rsquo;.  <span class="sc">gdb</span> 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><span class="sc">gdb</span> performs argument-dependent lookup, following the C<tt>++</tt>
specification.
        </ol>

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