123 lines
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123 lines
6.9 KiB
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<title>C Plus Plus Expressions - Debugging with GDB</title>
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<div class="node">
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<a name="C-Plus-Plus-Expressions"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="C-Defaults.html#C-Defaults">C Defaults</a>,
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Previous: <a rel="previous" accesskey="p" href="C-Constants.html#C-Constants">C Constants</a>,
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Up: <a rel="up" accesskey="u" href="C.html#C">C</a>
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<hr>
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</div>
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<h5 class="subsubsection">15.4.1.3 C<tt>++</tt> Expressions</h5>
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<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.
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<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>
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<em>Warning:</em> <span class="sc">gdb</span> can only debug C<tt>++</tt> code if you use
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the proper compiler and the proper debug format. Currently,
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<span class="sc">gdb</span> works best when debugging C<tt>++</tt> code that is compiled
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with the most recent version of <span class="sc">gcc</span> possible. The DWARF
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debugging format is preferred; <span class="sc">gcc</span> defaults to this on most
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popular platforms. Other compilers and/or debug formats are likely to
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work badly or not at all when using <span class="sc">gdb</span> to debug C<tt>++</tt>
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code. See <a href="Compilation.html#Compilation">Compilation</a>.
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</blockquote>
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<ol type=1 start=1>
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<p><a name="index-member-functions-993"></a><li>Member function calls are allowed; you can use expressions like
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<pre class="smallexample"> count = aml->GetOriginal(x, y)
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</pre>
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<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
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expressions have the same namespace available as the member function;
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that is, <span class="sc">gdb</span> allows implicit references to the class instance
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pointer <code>this</code> following the same rules as C<tt>++</tt>. <code>using</code>
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declarations in the current scope are also respected by <span class="sc">gdb</span>.
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<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
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call to the right definition, with some restrictions. <span class="sc">gdb</span> does not
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perform overload resolution involving user-defined type conversions,
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calls to constructors, or instantiations of templates that do not exist
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in the program. It also cannot handle ellipsis argument lists or
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default arguments.
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<p>It does perform integral conversions and promotions, floating-point
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promotions, arithmetic conversions, pointer conversions, conversions of
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class objects to base classes, and standard conversions such as those of
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functions or arrays to pointers; it requires an exact match on the
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number of function arguments.
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<p>Overload resolution is always performed, unless you have specified
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<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>.
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<p>You must specify <code>set overload-resolution off</code> in order to use an
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explicit function signature to call an overloaded function, as in
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<pre class="smallexample"> p 'foo(char,int)'('x', 13)
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</pre>
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<p>The <span class="sc">gdb</span> command-completion facility can simplify this;
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see <a href="Completion.html#Completion">Command Completion</a>.
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<p><a name="index-reference-declarations-999"></a><li><span class="sc">gdb</span> understands variables declared as C<tt>++</tt> lvalue or rvalue
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references; you can use them in expressions just as you do in C<tt>++</tt>
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source—they are automatically dereferenced.
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<p>In the parameter list shown when <span class="sc">gdb</span> displays a frame, the values of
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reference variables are not displayed (unlike other variables); this
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avoids clutter, since references are often used for large structures.
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The <em>address</em> of a reference variable is always shown, unless
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you have specified ‘<samp><span class="samp">set print address off</span></samp>’.
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<li><span class="sc">gdb</span> supports the C<tt>++</tt> name resolution operator <code>::</code>—your
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expressions can use it just as expressions in your program do. Since
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one scope may be defined in another, you can use <code>::</code> repeatedly if
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necessary, for example in an expression like
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‘<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
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resolving name scope by reference to source files, in both C and C<tt>++</tt>
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debugging (see <a href="Variables.html#Variables">Program Variables</a>).
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<li><span class="sc">gdb</span> performs argument-dependent lookup, following the C<tt>++</tt>
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specification.
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</ol>
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</body></html>
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