Printable View
I have a class that inherits many variables from the parent. The program works in that all the variables are accessable in the program.
I am having a problem viewing the data in GDB. A place holder comes up but reports no data. Is there a flag I need to compile with or start gdb with or something? Any help or guidance is appreciated.
I am using: Suse 10.1, gcc 4.1.0-25, gdb 6.4.19
I have tried the variables in the top class as protected (first) and public.
There doesn't seem to be anything special necessary, for me at least.
Note that I'm sure you'd need to compile all of your source files with debugging information available. Also, if you have a pointer to a base class which actually points to a derived class, you may need to cast the pointer if you want to see derived class data; but this doesn't seem to be your problem.Code:$ cat basegdb.cpp
#include <iostream>
class object {
private:
int id;
public:
object(int id) : id(id) {}
};
class physical_object : public object {
private:
bool solid;
public:
physical_object(int id, bool solid) : object(id), solid(solid) {}
};
int main() {
physical_object o(42, true);
return 0;
}
$ g++ -g basegdb.cpp -o basegdb
$ gdb ./basegdb
GNU gdb Red Hat Linux (6.5-37.el5_2.2rh)
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i386-redhat-linux-gnu"...Using host libthread_db library "/lib/libthread_db.so.1".
(gdb) break main
Breakpoint 1 at 0x8048535: file basegdb.cpp, line 18.
(gdb) r
Starting program: ./basegdb
Breakpoint 1, main () at basegdb.cpp:18
18 physical_object o(42, true);
(gdb) n
19 return 0;
(gdb) p o
$1 = {<object> = {id = 42}, solid = true}
(gdb)
Quote:
Originally Posted by dwks
The gdb output is from memory, but basicly what it reports. I can see all the data in the physical_object class except for the base class data. I compile with -g3, -dwarf-2 -WallCode:class object {
private:
int id;
public:
object(int id) : id(id) {}
int myBaseData;
};
class physical_object : public object {
private:
bool solid;
public:
physical_object(int id, bool solid) : object(id), solid(solid) {}
void editBaseData(int newData){myBaseData = newData;};
};
int main() {
physical_object o(42, true);
o.editBaseData(5);
return 0;
}
$ g++ -g basegdb.cpp -o basegdb
$ gdb ./basegdb
(gdb) break main
Breakpoint 1 at 0x8048535: file basegdb.cpp, line 18.
(gdb) r
Starting program: ./basegdb
Breakpoint 1, main () at basegdb.cpp:18
18 physical_object o(42, true);
(gdb) n
19 return 0;
(gdb) p o
$1 = {<> = no data}
(gdb)
I'm assuming you mean -g3 -gdwarf-2 -Wall?
Anyway, I can't think of what might be wrong. I can only suggest that you try a simple example like the one I have posted, and if that works but your code doesn't, then it must be the way in which your project is being built.
Or gdb is not working as it should.Quote:
Originally Posted by dwks
--
Mats
Perhaps. Have you ever used GDB in this way before?
Also: http://developer.apple.com/documenta...db/gdb_14.html
Maybe you could try turning that setting on? . . . .Code:set opaque-type-resolution off
Tell GDB not to resolve opaque types. In this case, the type is printed as follows:
{<no data fields>}
This isn't very helpful. http://osdir.com/ml/gdb.bugs.discuss.../msg00016.html Your version of GDB looks reasonably recent, though I have 6.8 myself.
Quote:
Originally Posted by dwks
Of course gdwarf-2.
I tried a generic class/subclass program and it worked fine. I guess it is something I am doing not quite right.
Thanks for the help...
If you want to get to the bottom of the problem, try to reduce your existing large project and strip it down to the minimum of what is needed to reproduce it. If you can produce something relatively small that can reproduce the problem, then I'd say post it here. And unless someone comes up with an immediate solution (which may be "upgrade to GDB version x"), then it's time to post it to the GDB bugzilla or some such. [Of course, it could be the compiler generating crap debug info too!].Quote:
Originally Posted by markcole
--
Mats
Well I "figured out" what is wrong. Kind of.
The base class has some virtual functions in it and therefore I had the destructor declared as virtual. Additionally, I have the base class compiled as a library and it is linked to the main project.
When the destructor is declared as virtual I cannot see the data in GDB. If the destructor is not declared virtual, I CAN see the data fields.
I am not sure why. If anyone has any hints or suggestions I would be greatful.
I realize this is less a C++ issue/question and more a GDB/gcc question, but thanks for the assistance any who.
Obvious/stupid question: Is your library compiled with debug info too?
--
Mats
Normally I would agree that it is a "Obvious/stupid question", however in this case...Quote:
Originally Posted by matsp
Thanks for the second set of eyes.