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(gdb.info)C plus plus expressions

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C++ expressions
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   GDB expression handling can interpret most C++ expressions.

     _Warning:_ GDB can only debug C++ code if you use the proper
     compiler.  Typically, C++ debugging depends on the use of
     additional debugging information in the symbol table, and thus
     requires special support.  In particular, if your compiler
     generates a.out, MIPS ECOFF, RS/6000 XCOFF, or ELF with stabs
     extensions to the symbol table, these facilities are all
     available.  (With GNU CC, you can use the `-gstabs' option to
     request stabs debugging extensions explicitly.)  Where the object
     code format is standard COFF or DWARF in ELF, on the other hand,
     most of the C++ support in GDB does _not_ work.

  1. Member function calls are allowed; you can use expressions like

          count = aml->GetOriginal(x, y)

  2. While a member function is active (in the selected stack frame),
     your expressions have the same namespace available as the member
     function; that is, GDB allows implicit references to the class
     instance pointer `this' following the same rules as C++.

  3. You can call overloaded functions; GDB resolves the function call
     to the right definition, with some restrictions.  GDB 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.

     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.

     Overload resolution is always performed, unless you have specified
     `set overload-resolution off'.  *Note GDB features for C++:
     Debugging C plus plus.

     You must specify `set overload-resolution off' in order to use an
     explicit function signature to call an overloaded function, as in
          p 'foo(char,int)'('x', 13)

     The GDB command-completion facility can simplify this; see Note:
     Command completion.

  4. GDB understands variables declared as C++ references; you can use
     them in expressions just as you do in C++ source--they are
     automatically dereferenced.

     In the parameter list shown when GDB 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 _address_ of a reference variable is always
     shown, unless you have specified `set print address off'.

  5. GDB supports the C++ name resolution operator `::'--your
     expressions can use it just as expressions in your program do.
     Since one scope may be defined in another, you can use `::'
     repeatedly if necessary, for example in an expression like
     `SCOPE1::SCOPE2::NAME'.  GDB also allows resolving name scope by
     reference to source files, in both C and C++ debugging (Note:
     Program variables.).

   In addition, when used with HP's C++ compiler, GDB supports calling
virtual functions correctly, printing out virtual bases of objects,
calling functions in a base subobject, casting objects, and invoking
user-defined operators.