Re: memory allocation in GLIB

[Tristan Van Berkom <vantr touchtunes com>]

martyn 2 russell bt com wrote:
> > I have a problem (SEGFAULT) when freeing a vector allocated using
> > routines in GLIB (version 1.2.10).
> >
> > I declare my variable as:
> >       gfloat *vector;
>
> Just as a word of advise, it is usually best to initialise pointers to NULL
> and check for NULL before you free them, and generally, when I have free'd a
> pointer, I set it to NULL afterwards.  This way I should never get into a
> situation where I am freeing memory already free'd and I know if it is being
> used based on the pointers value.
>
> Just makes me cringe when I see unintialised pointers :S
        It seems to be the latest trend to assume that
memory allocation doesn't fail :/ (not only in glib et al)
personaly (hard headed me) I still encapsulate all
functions with return codes in `if's i.e.

if ((ptr = g_strdup_printf("%s bla bla bla", sting)) != NULL) {
        // use string
        g_free(ptr);
}

I guess in a futile hope to be able to someday do:
./configure --disable-goddamn-abort()-in-g_malloc()-calls

or just because I think it looks right.


> > I then allocate memory as:
> >       vector = g_malloc ( (some_int)*sizeof(gfloat) );
> >
> > This allows me to access the memory using:
> >       for (i=0; i<(some_int); i++)  vector[i] = some_float;
> >
> > then when exiting the function, I free the memory using:
> >       g_free( vector );
> >
> > This statement causes a SEGFAULT.  Can anyone suggest what I am doing
> > wrong.
>
> Also, what does a back trace report from gdb?


================ from other mail ... ====================
> That is one of my problems, This particular routine is in a plug-in, 
> and I have not figured out how to debug
> shared libraries with gdb.  :-(
>
> I figure I need to give gdb a path to the directory, something like ...
>
>         LD_LIBRARY_PATH = '/path_to_directory/lib'
>
> Thanks for the advice.


AFAIK as long as you're executable can find
the symbols it needs; gdb will find them too.

I have had problems single-stepping into shared
libraries in the past though.

you might want to try 

nm shared_library | grep symbol

and add a breakpoint at the address
yielded from nm. (hmm I'm not sure if
you had to add a value to that address).

HTH,
                -Tristan