GDB Printers: Unintialized variable in gdb

[Ralf Habacker]

Am 24.08.21 um 17:27 schrieb Da Viper via Kde-finance-apps:
> There is a QDateTime  printer that requires calling a method  to get 
> useful values.
>
> The problem is when I call the method from gdb the printer crashes 
> because the variable does not exist yet thus the method does not exist 
> in memory.

The gdb Xmethods support may help, from https://sourceware.org/gdb/current/onlinedocs/gdb/Xmethods-In-Python.html

/Xmethods/  are additional methods or replacements for existing
methods of a C++  class.  This feature is useful for those cases
where a method defined in C++  source code could be inlined or
optimized out by the compiler, making it unavailable toGDB.
For such cases, one can define an xmethod to serve as a replacement
for the method defined in the C++  source code.GDB  will
then invoke the xmethod, instead of the C++  method, to
evaluate expressions.

>
> Is there a way to check if a variable has been initialised ?

In gdb access to invalid variables is catched

(gdb) x 0
0x0:    Cannot access memory at address 0x0

which can also be used by python

(gdb) python gdb.execute('x 0')
Traceback (most recent call last):
   File "<string>", line 1, in <module>
gdb.MemoryError: Cannot access memory at address 0x0
0x0:    Error while executing Python code.

Wrapping this code with a try/catch block should do this, e.g.

(gdb) python
 >try:
 >    gdb.execute('x 0')
 >except:
 >    print('exception')
 >end
0x0:    exception

Regards

Ralf


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