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<title>Debugging with GDB: C Plus Plus Expressions</title>
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<a name="C-Plus-Plus-Expressions"></a>
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<div class="header">
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<p>
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Next: <a href="C-Defaults.html#C-Defaults" accesskey="n" rel="next">C Defaults</a>, Previous: <a href="C-Constants.html#C-Constants" accesskey="p" rel="previous">C Constants</a>, Up: <a href="C.html#C" accesskey="u" rel="up">C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="C_002b_002b-Expressions"></a>
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<h4 class="subsubsection">15.4.1.3 C<tt>++</tt> Expressions</h4>
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<a name="index-expressions-in-C_002b_002b"></a>
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<p><small>GDB</small> expression handling can interpret most C<tt>++</tt> expressions.
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</p>
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<a name="index-debugging-C_002b_002b-programs"></a>
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<a name="index-C_002b_002b-compilers"></a>
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<a name="index-debug-formats-and-C_002b_002b"></a>
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<a name="index-GCC-and-C_002b_002b"></a>
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<blockquote>
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<p><em>Warning:</em> <small>GDB</small> 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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<small>GDB</small> works best when debugging C<tt>++</tt> code that is compiled
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with the most recent version of <small>GCC</small> possible. The DWARF
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debugging format is preferred; <small>GCC</small> 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 <small>GDB</small> to debug C<tt>++</tt>
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code. See <a href="Compilation.html#Compilation">Compilation</a>.
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</p></blockquote>
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<ol>
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<li> <a name="index-member-functions"></a>
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Member function calls are allowed; you can use expressions like
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<div class="smallexample">
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<pre class="smallexample">count = aml->GetOriginal(x, y)
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</pre></div>
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</li><li> <a name="index-this_002c-inside-C_002b_002b-member-functions"></a>
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<a name="index-namespace-in-C_002b_002b"></a>
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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, <small>GDB</small> 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 <small>GDB</small>.
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</li><li> <a name="index-call-overloaded-functions"></a>
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<a name="index-overloaded-functions_002c-calling"></a>
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<a name="index-type-conversions-in-C_002b_002b"></a>
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You can call overloaded functions; <small>GDB</small> resolves the function
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call to the right definition, with some restrictions. <small>GDB</small> 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>
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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"><small>GDB</small> Features for C<tt>++</tt></a>.
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</p>
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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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</p><div class="smallexample">
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<pre class="smallexample">p 'foo(char,int)'('x', 13)
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</pre></div>
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<p>The <small>GDB</small> command-completion facility can simplify this;
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see <a href="Completion.html#Completion">Command Completion</a>.
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</p>
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</li><li> <a name="index-reference-declarations"></a>
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<small>GDB</small> 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 <small>GDB</small> 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>set print address off</samp>’.
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</p>
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</li><li> <small>GDB</small> 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>::<var>scope2</var>::<var>name</var></samp>’. <small>GDB</small> 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><li> <small>GDB</small> performs argument-dependent lookup, following the C<tt>++</tt>
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specification.
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</li></ol>
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<hr>
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<div class="header">
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<p>
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Next: <a href="C-Defaults.html#C-Defaults" accesskey="n" rel="next">C Defaults</a>, Previous: <a href="C-Constants.html#C-Constants" accesskey="p" rel="previous">C Constants</a>, Up: <a href="C.html#C" accesskey="u" rel="up">C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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