This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of C++14 status.
regex_constants::nosubs affect basic_regex::mark_count()?Section: 28.6.4.2 [re.synopt] Status: C++14 Submitter: Jonathan Wakely Opened: 2014-02-01 Last modified: 2017-09-07
Priority: 0
View all other issues in [re.synopt].
View all issues with C++14 status.
Discussion:
As discussed in c++std-lib-35399 and its replies,
I can see two possible interpretations of the effects of regex_constants::nosubs:
The effect of nosubs only applies during matching. Parentheses are
still recognized as marking a sub-expression by the basic_regex
compiler, and basic_regex::mark_count() still returns the number of
marked sub-expressions, but anything they match is not stored in the
results. This means it is not always true that results.size() == r.mark_count() + 1
for a successful match.
nosubs affects how a regular expression is compiled, altering the
state of the std::basic_regex object so that mark_count() returns
zero. This also affects any subsequent matching.
The definition of nosubs should make this clear.
The wording in 28.6.4.2 [re.synopt]/1 seems to imply that nosubs only has
effects during matching, which is (1), but all known implementations
do (2). John Maddock confirmed that (2) was intended.
[Issaquah 2014-02-12: Move to Immediate]
Proposed resolution:
This wording is relative to N3797.
Apply the following edit to the table in 28.6.4.2 [re.synopt]/1
Specifies that no sub-expressions shall be considered to be marked, so that when a regular expression is matched against a character container sequence, no sub-expression matches shall be stored in the supplied
match_resultsstructure.