Re: Bug in String Height

[Shlomi Fish <shlomif vipe technion ac il>]

On Wed, 16 May 2001, Pavel Rousnak wrote:

> Hi all!
>
> I'm using Gtk 0.7006.
>
> There is a bug in Gtk::Gdk::Font::string_height() causing 'segmentation fault'
> when I call this function.
> At the same time text_height() works perfectly.
>
> Examining Gtk.xs I've found out the following:
> There is a line:
>  RETVAL = gdk_text_height(font, SvPV(text, tlen), ix==1?len:tlen); 
> which is buggy (in my opinion, of course). 
> Compiler doesn't guarantee that parameters are calculating in order they 
> appear in the list (from left to right). 
> My gcc 2.96, for example, passes them in opposite order, so function
> gdk_text_height will be passed undefined value as third parameter because
> it is pushed to the stack earlier than SvPV is called.

Just my uneducated opinion but I think that from the definition of C
SvPv(text, tlen) _must_ be evaluated before gdk_text_height is called. If
your compiler does not do that then it is buggy, and it is not the fault
of the Perl/Gtk+ bindings.

Whether SvPv(text, tlen) is evaluated before "ix==1?len:tlen" or not is
left to the discretion of the compiler, but otherwise arguments to
functions are processed before the functions themselves.
 
Regards,

        Shlomi Fish

> It seems to me there are more functions with the same bug (at least 
> gdk_string_extents() contains similar line).
>
>
> -- 
>
> Best regards
> Pavel.
>
>
>
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----------------------------------------------------------------------
Shlomi Fish        shlomif vipe technion ac il 
Home Page:         http://t2.technion.ac.il/~shlomif/
Home E-mail:       shlomif techie com

A more experienced programmer does not make less bugs. He just realizes
what went wrong more quickly.