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<h5 class="subsubsection">15.4.1.7 <span class="sc">gdb</span> Features for C<tt>++</tt></h5>

<p><a name="index-commands-for-C_0040t_007b_002b_002b_007d-1002"></a>
Some <span class="sc">gdb</span> commands are particularly useful with C<tt>++</tt>, and some are
designed specifically for use with C<tt>++</tt>.  Here is a summary:

     
<a name="index-break-in-overloaded-functions-1003"></a>
<dl><dt><span class="roman">breakpoint menus</span><dd>When you want a breakpoint in a function whose name is overloaded,
<span class="sc">gdb</span> has the capability to display a menu of possible breakpoint
locations to help you specify which function definition you want. 
See <a href="Ambiguous-Expressions.html#Ambiguous-Expressions">Ambiguous Expressions</a>.

     <p><a name="index-overloading-in-C_0040t_007b_002b_002b_007d-1004"></a><br><dt><code>rbreak </code><var>regex</var><dd>Setting breakpoints using regular expressions is helpful for setting
breakpoints on overloaded functions that are not members of any special
classes. 
See <a href="Set-Breaks.html#Set-Breaks">Setting Breakpoints</a>.

     <p><a name="index-C_0040t_007b_002b_002b_007d-exception-handling-1005"></a><br><dt><code>catch throw</code><dt><code>catch rethrow</code><dt><code>catch catch</code><dd>Debug C<tt>++</tt> exception handling using these commands.  See <a href="Set-Catchpoints.html#Set-Catchpoints">Setting Catchpoints</a>.

     <p><a name="index-inheritance-1006"></a><br><dt><code>ptype </code><var>typename</var><dd>Print inheritance relationships as well as other information for type
<var>typename</var>. 
See <a href="Symbols.html#Symbols">Examining the Symbol Table</a>.

     <br><dt><code>info vtbl </code><var>expression</var><code>.</code><dd>The <code>info vtbl</code> command can be used to display the virtual
method tables of the object computed by <var>expression</var>.  This shows
one entry per virtual table; there may be multiple virtual tables when
multiple inheritance is in use.

     <p><a name="index-C_0040t_007b_002b_002b_007d-demangling-1007"></a><br><dt><code>demangle </code><var>name</var><dd>Demangle <var>name</var>. 
See <a href="Symbols.html#Symbols">Symbols</a>, for a more complete description of the <code>demangle</code> command.

     <p><a name="index-C_0040t_007b_002b_002b_007d-symbol-display-1008"></a><br><dt><code>set print demangle</code><dt><code>show print demangle</code><dt><code>set print asm-demangle</code><dt><code>show print asm-demangle</code><dd>Control whether C<tt>++</tt> symbols display in their source form, both when
displaying code as C<tt>++</tt> source and when displaying disassemblies. 
See <a href="Print-Settings.html#Print-Settings">Print Settings</a>.

     <br><dt><code>set print object</code><dt><code>show print object</code><dd>Choose whether to print derived (actual) or declared types of objects. 
See <a href="Print-Settings.html#Print-Settings">Print Settings</a>.

     <br><dt><code>set print vtbl</code><dt><code>show print vtbl</code><dd>Control the format for printing virtual function tables. 
See <a href="Print-Settings.html#Print-Settings">Print Settings</a>. 
(The <code>vtbl</code> commands do not work on programs compiled with the HP
ANSI C<tt>++</tt> compiler (<code>aCC</code>).)

     <p><a name="index-set-overload_002dresolution-1009"></a><a name="index-overloaded-functions_002c-overload-resolution-1010"></a><br><dt><code>set overload-resolution on</code><dd>Enable overload resolution for C<tt>++</tt> expression evaluation.  The default
is on.  For overloaded functions, <span class="sc">gdb</span> evaluates the arguments
and searches for a function whose signature matches the argument types,
using the standard C<tt>++</tt> conversion rules (see <a href="C-Plus-Plus-Expressions.html#C-Plus-Plus-Expressions">C<tt>++</tt> Expressions</a>, for details). 
If it cannot find a match, it emits a message.

     <br><dt><code>set overload-resolution off</code><dd>Disable overload resolution for C<tt>++</tt> expression evaluation.  For
overloaded functions that are not class member functions, <span class="sc">gdb</span>
chooses the first function of the specified name that it finds in the
symbol table, whether or not its arguments are of the correct type.  For
overloaded functions that are class member functions, <span class="sc">gdb</span>
searches for a function whose signature <em>exactly</em> matches the
argument types.

     <p><a name="index-show-overload_002dresolution-1011"></a><br><dt><code>show overload-resolution</code><dd>Show the current setting of overload resolution.

     <br><dt><span class="roman">Overloaded symbol names</span><dd>You can specify a particular definition of an overloaded symbol, using
the same notation that is used to declare such symbols in C<tt>++</tt>: type
<var>symbol</var><code>(</code><var>types</var><code>)</code> rather than just <var>symbol</var>.  You can
also use the <span class="sc">gdb</span> command-line word completion facilities to list the
available choices, or to finish the type list for you. 
See <a href="Completion.html#Completion">Command Completion</a>, for details on how to do this.

     <br><dt><span class="roman">Breakpoints in functions with ABI tags</span><dd>
The GNU C<tt>++</tt> compiler introduced the notion of ABI &ldquo;tags&rdquo;, which
correspond to changes in the ABI of a type, function, or variable that
would not otherwise be reflected in a mangled name.  See
<a href="https://developers.redhat.com/blog/2015/02/05/gcc5-and-the-c11-abi/">https://developers.redhat.com/blog/2015/02/05/gcc5-and-the-c11-abi/</a>
for more detail.

     <p>The ABI tags are visible in C<tt>++</tt> demangled names.  For example, a
function that returns a std::string:

     <pre class="smallexample">          std::string function(int);
</pre>
     <p class="noindent">when compiled for the C++11 ABI is marked with the <code>cxx11</code> ABI
tag, and <span class="sc">gdb</span> displays the symbol like this:

     <pre class="smallexample">          function[abi:cxx11](int)
</pre>
     <p>You can set a breakpoint on such functions simply as if they had no
tag.  For example:

     <pre class="smallexample">          (gdb) b function(int)
          Breakpoint 2 at 0x40060d: file main.cc, line 10.
          (gdb) info breakpoints
          Num     Type           Disp Enb Address    What
          1       breakpoint     keep y   0x0040060d in function[abi:cxx11](int)
                                                     at main.cc:10
</pre>
     <p>On the rare occasion you need to disambiguate between different ABI
tags, you can do so by simply including the ABI tag in the function
name, like:

     <pre class="smallexample">          (gdb) b ambiguous[abi:other_tag](int)
</pre>
     </dl>

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