Re: Option to elide single-bit bitfields when printing structures

[Daniel Berlin <dberlin at redhat dot com>]

Eli Zaretskii <eliz@delorie.com> writes:

> > From: "Zack Weinberg" <zackw@stanford.edu>
> > Date: Thu, 22 Feb 2001 11:56:33 -0800
> > 
> > (gdb) p decl->common
> > $1 = {chain = 0x40253000, type = 0x40253138, code = FUNCTION_DECL, 
> >   side_effects_flag = 0, constant_flag = 0, addressable_flag = 0, 
> >   volatile_flag = 0, readonly_flag = 0, unsigned_flag = 0, 
> >   asm_written_flag = 0, used_flag = 0, nothrow_flag = 0, static_flag = 0, 
> >   public_flag = 1, private_flag = 0, protected_flag = 0, bounded_flag = 0, 
> >   lang_flag_0 = 0, lang_flag_1 = 0, lang_flag_2 = 0, lang_flag_3 = 0, 
> >   lang_flag_4 = 0, lang_flag_5 = 0, lang_flag_6 = 0, dummy = 0}
> > 
> > It's hard to see which are set and which aren't.  With this patch, you
> > can get it printed like this:
> > 
> > (gdb) set print elide-bitflags on
> > (gdb) p decl->common
> > $2 = {chain = 0x40253000, type = 0x40253138, code = FUNCTION_DECL, public_flag}
> > 
> > which is, IMHO, much easier to read.
> 
> What if someone wants to know which flags are _reset_?

Nobody really does, it wouldn't make sense.
You know what isn't set because it's not shown.

>  What if there
> are more than one set flag in your example?
There is.
>  What if the bit fields
> span more than one bit?

It prints them the normal way.

>  I don't see how your suggestion would deal
> with these cases in a way that the resulting display is
> self-explaining.  That trailing "public_flag" is already hard to
> understand; I stared at it for a few moments without understanding
> what's going on here, before it hit me.
> 
> Perhaps we need a special command or a special format that would put
> the burden on the user.  For example, if the user specifies exactly
> what flags (set or unset) does she want to see, the display doesn't
> need to explain that, because the user asked for it.

Errr, it only elides the display if you set a command specifically.
It defaults to the old behavior.