Debugging with GDB (September 2007)

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 doe s 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 numbe r 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 spec iﬁed ‘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 {