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SubjectRe: sscanf: implement basic character sets
+++ 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@redhat.com>
>> ---
>>  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

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