Cannot access memory at address 0x0

**defumar** · 25th January 2008, 15:57

behold:
(gdb) bt
#0 main (argc=Cannot access memory at address 0x0
) at main.cpp:7
^done

**wysota** · 25th January 2008, 17:47

How exactly did you compile the application? What happens if you change "*argv[]" to "**argv"? I know the former should work but it should all work and it doesn't so I'm curious to see the result.

**defumar** · 26th January 2008, 09:17

Firstly I went into the src directory of my Simple Qt project and I ran qmake -project and qmake, then I opened up KDevelop again and had it Build Project using all the default settings for a qmake project. (g++)
I tried changing it to ** but still got the same error.

**wysota** · 26th January 2008, 10:22

What is the contents of the .pro file?

**defumar** · 26th January 2008, 10:27

Qt Code:

Switch view

SUBDIRS += src
TEMPLATE = subdirs 
CONFIG += warn_on \
          qt \
          thread

SUBDIRS += src
TEMPLATE = subdirs 
CONFIG += warn_on \
          qt \
          thread

To copy to clipboard, switch view to plain text mode

I read that the -fstack-check option may cause an error like this. I have no idea of where to find it in my KDevelop though.
The page I read this --> http://lists.trolltech.com/qt-intere.../msg00731.html

**wysota** · 26th January 2008, 10:38

What's the contents of the .pro file inside the src subdirectory?

Oh, and please rebuild your project without KDevelop. Open the console, cd into src, run qmake, make distclean, qmake, make.

**defumar** · 26th January 2008, 10:44

oh right, here it is:

Qt Code:

Switch view

######################################################################
# Automatically generated by qmake (2.01a) Fri Jan 25 13:56:09 2008
######################################################################
 
TEMPLATE = app
TARGET = 
DEPENDPATH += .
INCLUDEPATH += .
 
# Input
SOURCES += main.cpp

######################################################################
# Automatically generated by qmake (2.01a) Fri Jan 25 13:56:09 2008
######################################################################

TEMPLATE = app
TARGET = 
DEPENDPATH += .
INCLUDEPATH += .

# Input
SOURCES += main.cpp

To copy to clipboard, switch view to plain text mode

Right I made it without KDevelop and this is what gdb gave me when stepping through code.

Qt Code:

Switch view

~/MToDo/src$ gdb src
GNU gdb 6.6-debian
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 "i486-linux-gnu"...
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
(gdb) break main
Breakpoint 1 at 0x8048596: file main.cpp, line 5.
(gdb) run
Starting program: /home/defumar/MToDo/src/src 
[Thread debugging using libthread_db enabled]
[New Thread -1224051008 (LWP 6910)]
[Switching to Thread -1224051008 (LWP 6910)]
 
Breakpoint 1, main (argc=1, argv=0xbfb26af4) at main.cpp:5
5               QApplication app(argc, argv);
(gdb) n
Qt: gdb: -nograb added to command-line options.
         Use the -dograb option to enforce grabbing.
7               return 0;
(gdb) n
8       }
(gdb) n
0xb743b050 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
(gdb) n
Single stepping until exit from function __libc_start_main, 
which has no line number information.
 
Program exited normally.
(gdb) q

~/MToDo/src$ gdb src
GNU gdb 6.6-debian
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 "i486-linux-gnu"...
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
(gdb) break main
Breakpoint 1 at 0x8048596: file main.cpp, line 5.
(gdb) run
Starting program: /home/defumar/MToDo/src/src 
[Thread debugging using libthread_db enabled]
[New Thread -1224051008 (LWP 6910)]
[Switching to Thread -1224051008 (LWP 6910)]

Breakpoint 1, main (argc=1, argv=0xbfb26af4) at main.cpp:5
5               QApplication app(argc, argv);
(gdb) n
Qt: gdb: -nograb added to command-line options.
         Use the -dograb option to enforce grabbing.
7               return 0;
(gdb) n
8       }
(gdb) n
0xb743b050 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
(gdb) n
Single stepping until exit from function __libc_start_main, 
which has no line number information.

Program exited normally.
(gdb) q

To copy to clipboard, switch view to plain text mode

backtrace after executing line 5 (evil line, ain't it) returns the same as before (argc=Cannot access mem at 0x0)

**wysota** · 26th January 2008, 12:57

From the above output it seems the program executes correctly. Or am I wrong?

**defumar** · 26th January 2008, 13:59

The above output shows that the program seems to execute correctly but in a different gdb session I backtraced a couple of times and noticed that after line 5 argc=Cannot access mem at 0x0
Which doesn't seem correct to me though. argc should still be valid as it was at line 5. Instead it shows that apparantly it got corrupted :\ Correct me if I'm wrong.

**wysota** · 26th January 2008, 15:43

Could you show us a print from a gdb session that segfaults the project? And are you sure this is not actually gdb that segfaults and not the project?

**defumar** · 26th January 2008, 16:07

Qt Code:

Switch view

~/MToDo/src$ gdb src
GNU gdb 6.6-debian
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 "i486-linux-gnu"...
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
(gdb) break main
Breakpoint 1 at 0x8048596: file main.cpp, line 5.
(gdb) run
Starting program: /home/defumar/MToDo/src/src 
[Thread debugging using libthread_db enabled]
[New Thread -1224476992 (LWP 6527)]
[Switching to Thread -1224476992 (LWP 6527)]
 
Breakpoint 1, main (argc=1, argv=0xbf9218f4) at main.cpp:5
5               QApplication app(argc, argv);
(gdb) bt
#0  main (argc=1, argv=0xbf9218f4) at main.cpp:5
(gdb) n
Qt: gdb: -nograb added to command-line options.
         Use the -dograb option to enforce grabbing.
7               return 0;
(gdb) bt
#0  main (argc=Cannot access memory at address 0x0
) at main.cpp:7
(gdb) p argc
Cannot access memory at address 0x0
(gdb) n
8       }
(gdb) bt
#0  main (argc=0, argv=0xa9) at main.cpp:8
(gdb) n
0xb73d3050 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
(gdb) n
Single stepping until exit from function __libc_start_main, 
which has no line number information.
 
Program exited normally.

~/MToDo/src$ gdb src
GNU gdb 6.6-debian
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 "i486-linux-gnu"...
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
(gdb) break main
Breakpoint 1 at 0x8048596: file main.cpp, line 5.
(gdb) run
Starting program: /home/defumar/MToDo/src/src 
[Thread debugging using libthread_db enabled]
[New Thread -1224476992 (LWP 6527)]
[Switching to Thread -1224476992 (LWP 6527)]

Breakpoint 1, main (argc=1, argv=0xbf9218f4) at main.cpp:5
5               QApplication app(argc, argv);
(gdb) bt
#0  main (argc=1, argv=0xbf9218f4) at main.cpp:5
(gdb) n
Qt: gdb: -nograb added to command-line options.
         Use the -dograb option to enforce grabbing.
7               return 0;
(gdb) bt
#0  main (argc=Cannot access memory at address 0x0
) at main.cpp:7
(gdb) p argc
Cannot access memory at address 0x0
(gdb) n
8       }
(gdb) bt
#0  main (argc=0, argv=0xa9) at main.cpp:8
(gdb) n
0xb73d3050 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
(gdb) n
Single stepping until exit from function __libc_start_main, 
which has no line number information.

Program exited normally.

To copy to clipboard, switch view to plain text mode

I am not sure whether the debugger messes up or the project itself, frankly I have no idea. Are there other debuggers I could try?

**wysota** · 26th January 2008, 17:22

It's not the QApplication constructor that segfaults, look that something happens at line 7. argc changes from 1 to 0. Do examples bundles with Qt build and run correctly? Are you able to run any Qt4 based application?

Thread: Cannot access memory at address 0x0

Thread Tools

Search Thread

Display

Hybrid View

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Re: Cannot access memory at address 0x0

Similar Threads

Memory leak weirdness

Memory Leak in my Application :-(

what is free store in C++ memory?

Qt 4.1.1 linker warnings

Bookmarks

Bookmarks

Posting Permissions