Re: sscanf: implement basic character sets

[Jessica Yu]

+++ Andy Shevchenko [22/02/16 12:13 +0200]:
> On Fri, 2016-02-19 at 20:22 -0500, Jessica Yu wrote:
> > Implement basic character sets for the '%[]' conversion specifier.
> >
> > The '%[]' conversion specifier matches a nonempty sequence of
> > characters
> > from the specified set of accepted (or with '^', rejected) characters
> > between the brackets. The substring matched is to be made up of
> > characters
> > in (or not in) the set. This implementation differs from its glibc
> > counterpart in that it does not support character ranges (e.g., 'a-z'
> > or
> > '0-9'), the hyphen '-' is *not* a special character, and the brackets
> > themselves cannot be matched.
> >
> > Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
> > ---
> >  lib/vsprintf.c | 35 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 35 insertions(+)
> >
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index 525c8e1..6ee3e7f 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -2714,6 +2714,41 @@ int vsscanf(const char *buf, const char *fmt,
> > va_list args)
> >  			num++;
> >  		}
> >  		continue;
> > +		case '[':
> > +		{
> > +			char *s = (char *)va_arg(args, char *);
> > +			char set[U8_MAX] = { 0 };
>
> Hmm... 255 on stack, not the best idea.
>
> > +			size_t (*op)(const char *str, const char
> > *set);
> > +			size_t len = 0;
> > +			bool negate = (*(fmt) == '^');
> > +
> > +			if (field_width == -1)
> > +				field_width = SHRT_MAX;
> > +
> > +			op = negate ? &strcspn : &strspn;
> > +			if (negate)
> > +				fmt++;
> > +
> > +			len = strcspn(fmt, "]");
> > +			/* invalid format; stop here */
> > +			if (!len)
> > +				return num;
> > +
> > +			strncpy(set, fmt, len);
>
> Perhaps here you may allocate memory on heap and copy the given set.
> IIRC kstrndup() does this.

Thanks for the comments Andy. I did in fact use kstrndup() originally,
but I was not sure about error handling. i.e., if kstrndup() fails we
normally return -ENOMEM, but in this case I suppose sscanf() could
just fail and return num?

Thanks,
Jessica