Re: coredump. dbx shows gtk internal functions.

On Thu, 03 Feb 2005 17:41:07 +0530, Mohan Kumar S said:
> coredump. dbx shows gtk internal functions. i cant figure out where &
> why it happens.Please help

> The program does coredump, which is not reprodusable.

> when i debug using dbx, "where"
> the most frequent one is this
> g_type_check_instance
> can anyone please tell, where there could be a problem
> (dbx)where
> [1] g_type_check_instance_is_a(0x6a678, 0x50a10, 0xfefce024, 0x7800,
> 0xff264cc4, 0x7a28), at 0xfefce02c

The single most important thing to remember for debugging this sort of thing
is that the coredump quite likely didn't actually happen anywhere near where the
bug is.  What's probably happened is that some *other* code, somewhere else in
the program, has overwritten data that g_type_check_instance() then used.

The most common causes of these sort of errors:

1) Going off the end of an array or string (storing into foo[50]; when
it's declared as 'int foo[50];', or strcat() or sprintf() writing more chars
than you allocated).

2) Abuse of a pointer - using the same value as a 'struct *foo' in one routine
and 'struct *bar' in another.  This is a lot harder to do without the compiler
whinging at you in recent C that uses ANSI function prototypes, but used to be
quite common in K&R C.

3) Using a pointer in one routine after you've done a free()  of it elsewhere
(causing indigestion for whoever got an malloc() there after the free().

4) Returning a pointer to a location on the returning function's stack.

How to debug this:

1) Get a clean compile.  Compile with 'gcc -Wall' and fix up the stuff it
complains about.

2) If your system has 'valgrind' installed, try using that - it will track
down a lot of memory-use errors.

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