Re: [PATCH v2 1/2] string: Add strprefix(), and deprecate str_has_prefix()

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Sun, Nov 08, 2026 at 12:54:33PM +0100, Alejandro Colomar wrote:
> > Date: 2026-11-08 12:49:08+0100
> > From: Alejandro Colomar <alx@kernel.org>
> >
> > Hi Maciej,
> > 
> > > Date: 2026-11-08 11:05:51+0000
> > > From: "Maciej W. Rozycki" <macro@orcam.me.uk>
> > >
> > > On Sat, 7 Nov 2026, Alejandro Colomar wrote:
> > > 
> > > > Hi Maciej,
> > > > 
> > > > > Date: 2026-11-07 02:44:23+0000
> > > > > From: "Maciej W. Rozycki" <macro@orcam.me.uk>
> > > > >
> > > > > On Thu, 5 Nov 2026, Alejandro Colomar wrote:
> > > > > 
> > > > > > Do you think strafterprefix() would be better?  Do you have any other
> > > > > > suggestions?
> > > > > 
> > > > >  FWIW strsuffix() seems an obvious choice to me.  After all what the API 
> > > > > does is request the string's suffix beyond the specified leading part.
> > > > 
> > > > Actually, strsuffix() is something else:
> > > > 
> > > > 	char *
> > > > 	strsuffix_(const char *str, const char *suffix)
> > > > 	{
> > > > 		ptrdiff_t  off;
> > > > 
> > > > 		off = strlen(str) - strlen(suffix);
> > > > 		if (off < 0)
> > > > 			return NULL;
> > > > 
> > > > 		if (!streq(str + off, suffix))
> > > > 			return NULL;
> > > > 
> > > > 		return str + off;
> > > > 	}
> > > > 
> > > > It finds the start of a suffix in a string.  That is:
> > > > 
> > > > 	strcmp(strsuffix("foobar", "bar"), "bar") == 0;
> > > 
> > >  Hmm, I'd have called that strskipto().  If that's not possible for some 
> > > reason (I can't see it used in Linux), then strskip() or strskipover() 
> > > could be used for this API.
> 
> Another issue with the name strskipto() is that the name doesn't make it
> clear whether the second argument is a string, or a list of characters.
> 
> That is, would strskipto() something similar to strpbrk(3)?
> It's not clear from the name.  From strprefix() and strsuffix(), the
> meaning of the second argument is clear from the function name.

On this bikeshedding thread I'm with Alejandro.

> > strsuffix() exists in many projects, and in all of them it seems to have
> > these semantics (or very similar ones).
> > 
> > Just look at a Debian code search of those names.
> > 
> > The strprefix() and strsuffix() pair of functions are widely
> > implemented, and while the exact details of the return value differ
> > slightly (some return just a boolean, others return a pointer that can
> > be used as a boolean too), the overall semantics of them are quite
> > consistent.  strsuffix() has less drift than strprefix().
> > 
> > If we added strsuffix() here with the semantics commonly attributed to
> > strprefix(), and then had strskipto() with the semantics commonly
> > attributed to strsuffix(), I'd expect programmers to eventually get
> > confused and use the wrong one. 

-- 
With Best Regards,
Andy Shevchenko