Обсуждение: regex Quantifiers {m,n}, m can be negative, n greater than 255

hi.

""
The forms using {...} are known as bounds. The numbers m and n within a bound
are unsigned decimal integers with permissible values from 0 to 255 inclusive.
""
Table (Regular Expression Quantifiers)
https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-POSIX-REGEXP

select regexp_matches(E'abc', 'a{0,257}.');
select regexp_matches(E'abc', 'a{-0,257}.');
select regexp_matches(E'abc', 'a{-1,2}.');

based on the manual description, the second and the third query should
error out?
test_regex.sql (begin with line 223) have many tests but no tests for
negative value.



--
jian
https://www.enterprisedb.com

jian he <jian.universality@gmail.com> writes:
> select regexp_matches(E'abc', 'a{0,257}.');
> select regexp_matches(E'abc', 'a{-0,257}.');
> select regexp_matches(E'abc', 'a{-1,2}.');

> based on the manual description, the second and the third query should
> error out?

No.  Read

https://www.postgresql.org/docs/current/functions-matching.html#POSIX-ATOMS-TABLE

which says that '{'

    when followed by a character other than a digit, matches the
    left-brace character {; when followed by a digit, it is the
    beginning of a bound (see below)

So your second and third patterns are just literal matches, except
for the final '.'.

You can quibble about how bright that choice was, but I think it's
mandated by POSIX, not just something that Henry Spencer thought up.

            regards, tom lane