Debugging with GDB (February 2008)

Chapter 9: Using GDB with Different Languages 87
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, arith-
metic 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 Section 9.4.1.7 [GDB features for C++], page 88.
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 Section 3.2 [Com-
mand completion], page 17.
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 vari-
ables 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 Section 8.2 [Program variables], page 64).
In addition, when used with the HP aC++ compiler, GDB supports calling virtual func-
tions 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 de-
fined 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:
‘RWCollectableDate d3(15,5,2001);’
printing the variable or class returns:
(gdb) p d3
$3 = {<No data fields>}
(gdb) ptype RWCollectableDate
type = class RWCollectableDate {
<no data fields>