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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-800"></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-801"></a><a name="index-C_0040t_007b_002b_002b_007d-compilers-802"></a><a name="index-debug-formats-and-C_0040t_007b_002b_002b_007d-803"></a><a name="index-g_t_0040value_007bNGCC_007d-and-C_0040t_007b_002b_002b_007d-804"></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 |
| <span class="sc">gcc</span> 2.95.3 or with <span class="sc">gcc</span> 3.1 or newer, using the options |
| <samp><span class="option">-gdwarf-2</span></samp> or <samp><span class="option">-gstabs+</span></samp>. DWARF 2 is preferred over |
| stabs+. Most configurations of <span class="sc">gcc</span> emit either DWARF 2 or |
| stabs+ as their default debug format, so you usually don't need to |
| specify a debug format explicitly. 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. |
| </blockquote> |
| |
| <ol type=1 start=1> |
| |
| <p><a name="index-member-functions-805"></a><li>Member function calls are allowed; you can use expressions like |
| |
| <pre class="smallexample"> count = aml->GetOriginal(x, y) |
| </pre> |
| <p><a name="index-this_0040r_007b_002c-inside-C_0040t_007b_002b_002b_007d-member-functions_007d-806"></a><a name="index-namespace-in-C_0040t_007b_002b_002b_007d-807"></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>. |
| |
| <p><a name="index-call-overloaded-functions-808"></a><a name="index-overloaded-functions_002c-calling-809"></a><a name="index-type-conversions-in-C_0040t_007b_002b_002b_007d-810"></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-811"></a><li><span class="sc">gdb</span> understands variables declared as C<tt>++</tt> references; you can use |
| them in expressions just as you do in C<tt>++</tt> source—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 ‘<samp><span class="samp">set print address off</span></samp>’. |
| |
| <li><span class="sc">gdb</span> supports the C<tt>++</tt> name resolution operator <code>::</code>—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 |
| ‘<samp><var>scope1</var><span class="samp">::</span><var>scope2</var><span class="samp">::</span><var>name</var></samp>’. <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>). |
| </ol> |
| |
| <p>In addition, when used with HP's C<tt>++</tt> compiler, <span class="sc">gdb</span> supports |
| calling virtual functions correctly, printing out virtual bases of |
| objects, calling functions in a base subobject, casting objects, and |
| invoking user-defined operators. |
| |
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