Debugging with GDB Manual HP WDB v6.3 (5900-2180, August 2012)

9.4.1.3 C++ expressions
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. See “GDB features for C++” (page 84).
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. Refer to “Command completion”
(page 27).
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 (see “Program variables” (page 63)).
In addition, when used with the HP aC++ 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.
NOTE: GDB cannot display debugging information for classes or functions defined in a shared
library that is not compiled for debugging (with the -g0 option). GDB displays the function with
the message <no data fields>.
For example, after 'd3' is created by the following line:
9.4 Supported languages 83