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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 “tags”, 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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