Cannot access memory at address 0x0

[defumar]

I think so as well. It only happens when I debug, yes.

Edit: aaargh, I downloaded gdb 6.7, compiled it, installed it, verified its version, tried to debug and yes, you can guess it alright. argc=cannot access mem at 0x0
So with a newer version it still acts weird... Might be some ubuntu issue still, I think.

[wysota]

gdb might only reveal the real problem which might be completely elsewhere. For instance in debug symbols of Qt or libc or some other library.

[Gopala Krishna]

Probably your qt build is corrupt i think. I closely looked at QApplication constructor and it uses
int reference for argc parameter. I dont know whether this is the problem or not but can you tell me where it crashes if you try the below program.

int main(int argc, char *argv[])
{
      int k = argc + 1;
      int l = argc;
      QApplication app(argc, argv);
      //also try QApplication(l, argv);
      return 0;
}

int main(int argc, char *argv[])
{
      int k = argc + 1;
      int l = argc;
      QApplication app(argc, argv);
      //also try QApplication(l, argv);
      return 0;
}

To copy to clipboard, switch view to plain text mode 

Also pay attention to this qapplication doc

Initializes the window system and constructs an application object with argc command line arguments in argv.

Warning: The data pointed to by argc and argv must stay valid for the entire lifetime of the QApplication object.

The global qApp pointer refers to this application object. Only one application object should be created.

This application object must be constructed before any paint devices (including widgets, pixmaps, bitmaps etc.).

Note that argc and argv might be changed. Qt removes command line arguments that it recognizes. The original argc and argv can be accessed later with arguments().

[defumar]

okay I tried both things and both of them got corrupted after the QApplication ctor (both having argc=cannot access 0x0)

[wysota]

The problem is clearly within gdb. If it was your application that was crashing you'd receive a different message from the debugger. Look that the "cannot access 0x0" message is received while the debugger tries to print the content of argc and not when executing any code from your application. The application doesn't crash when you don't debug it, so there is nothing wrong with it. Your debugger doesn't like your Qt installation or it doesn't like itself or your system. Either way your application is correct.

[Gopala Krishna]

Oh i just can't believe this! Even gdb on my comp shows the same thing for any program i debug(wysota, i tried your chip program )

And i use kubuntu.
Probably you are right wysota.

[wysota]

For the record - for me GDB works just fine

[defumar]

okay, so I installed SUSE 10.3 and on this one I get argc=1 before executing the ctor and argc=4 after executing the ctor and before exitting the function, according to gdb, is this correct or am I haunted?

[wysota]

Could be. QApplication takes its arguments by reference, so it is likely that it modifies them.

[defumar]

goodie, thanks for all the help