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153 lines
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<title>Debugging C Plus Plus - Debugging with GDB</title>
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<a name="Debugging-C-Plus-Plus"></a>
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Next: <a rel="next" accesskey="n" href="Decimal-Floating-Point.html#Decimal-Floating-Point">Decimal Floating Point</a>,
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Previous: <a rel="previous" accesskey="p" href="Debugging-C.html#Debugging-C">Debugging C</a>,
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Up: <a rel="up" accesskey="u" href="C.html#C">C</a>
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<h5 class="subsubsection">15.4.1.7 <span class="sc">gdb</span> Features for C<tt>++</tt></h5>
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<p><a name="index-commands-for-C_0040t_007b_002b_002b_007d-1002"></a>
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Some <span class="sc">gdb</span> commands are particularly useful with C<tt>++</tt>, and some are
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designed specifically for use with C<tt>++</tt>. Here is a summary:
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<a name="index-break-in-overloaded-functions-1003"></a>
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<dl><dt><span class="roman">breakpoint menus</span><dd>When you want a breakpoint in a function whose name is overloaded,
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<span class="sc">gdb</span> has the capability to display a menu of possible breakpoint
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locations to help you specify which function definition you want.
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See <a href="Ambiguous-Expressions.html#Ambiguous-Expressions">Ambiguous Expressions</a>.
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<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
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breakpoints on overloaded functions that are not members of any special
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classes.
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See <a href="Set-Breaks.html#Set-Breaks">Setting Breakpoints</a>.
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<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>.
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<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
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<var>typename</var>.
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See <a href="Symbols.html#Symbols">Examining the Symbol Table</a>.
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<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
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method tables of the object computed by <var>expression</var>. This shows
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one entry per virtual table; there may be multiple virtual tables when
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multiple inheritance is in use.
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<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>.
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See <a href="Symbols.html#Symbols">Symbols</a>, for a more complete description of the <code>demangle</code> command.
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<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
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displaying code as C<tt>++</tt> source and when displaying disassemblies.
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See <a href="Print-Settings.html#Print-Settings">Print Settings</a>.
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<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.
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See <a href="Print-Settings.html#Print-Settings">Print Settings</a>.
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<br><dt><code>set print vtbl</code><dt><code>show print vtbl</code><dd>Control the format for printing virtual function tables.
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See <a href="Print-Settings.html#Print-Settings">Print Settings</a>.
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(The <code>vtbl</code> commands do not work on programs compiled with the HP
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ANSI C<tt>++</tt> compiler (<code>aCC</code>).)
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<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
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is on. For overloaded functions, <span class="sc">gdb</span> evaluates the arguments
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and searches for a function whose signature matches the argument types,
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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).
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If it cannot find a match, it emits a message.
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<br><dt><code>set overload-resolution off</code><dd>Disable overload resolution for C<tt>++</tt> expression evaluation. For
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overloaded functions that are not class member functions, <span class="sc">gdb</span>
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chooses the first function of the specified name that it finds in the
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symbol table, whether or not its arguments are of the correct type. For
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overloaded functions that are class member functions, <span class="sc">gdb</span>
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searches for a function whose signature <em>exactly</em> matches the
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argument types.
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<p><a name="index-show-overload_002dresolution-1011"></a><br><dt><code>show overload-resolution</code><dd>Show the current setting of overload resolution.
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<br><dt><span class="roman">Overloaded symbol names</span><dd>You can specify a particular definition of an overloaded symbol, using
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the same notation that is used to declare such symbols in C<tt>++</tt>: type
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<var>symbol</var><code>(</code><var>types</var><code>)</code> rather than just <var>symbol</var>. You can
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also use the <span class="sc">gdb</span> command-line word completion facilities to list the
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available choices, or to finish the type list for you.
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See <a href="Completion.html#Completion">Command Completion</a>, for details on how to do this.
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<br><dt><span class="roman">Breakpoints in functions with ABI tags</span><dd>
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The GNU C<tt>++</tt> compiler introduced the notion of ABI “tags”, which
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correspond to changes in the ABI of a type, function, or variable that
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would not otherwise be reflected in a mangled name. See
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<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>
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for more detail.
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<p>The ABI tags are visible in C<tt>++</tt> demangled names. For example, a
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function that returns a std::string:
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<pre class="smallexample"> std::string function(int);
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</pre>
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<p class="noindent">when compiled for the C++11 ABI is marked with the <code>cxx11</code> ABI
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tag, and <span class="sc">gdb</span> displays the symbol like this:
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<pre class="smallexample"> function[abi:cxx11](int)
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</pre>
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<p>You can set a breakpoint on such functions simply as if they had no
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tag. For example:
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<pre class="smallexample"> (gdb) b function(int)
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Breakpoint 2 at 0x40060d: file main.cc, line 10.
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(gdb) info breakpoints
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Num Type Disp Enb Address What
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1 breakpoint keep y 0x0040060d in function[abi:cxx11](int)
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at main.cc:10
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</pre>
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<p>On the rare occasion you need to disambiguate between different ABI
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tags, you can do so by simply including the ABI tag in the function
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name, like:
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<pre class="smallexample"> (gdb) b ambiguous[abi:other_tag](int)
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</pre>
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</dl>
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