Why my subexpression doesn't work in Regex
Hello, I'm a new boost and regex user. I tried a c++ regex sample as follows regex pattern("banan\\(an\\)*a"); string str = "bananana"; if(regex_match(str, pattern)) cout<<"---- pattern matched ----"<<endl; else cout<<"---- pattern unmatched ----"<<endl; To my surprise, the it printed out pattern unmatched. If I change str to "banan(an)a", the result is pattern matched. Feels like boost.Regex doesn't treat ( ) as subexpression. Any idea? Thanks, Qihong Wang
AMDG Qihong Wang wrote:
I'm a new boost and regex user. I tried a c++ regex sample as follows
regex pattern("banan\\(an\\)*a"); string str = "bananana";
if(regex_match(str, pattern)) cout<<"---- pattern matched ----"<<endl; else cout<<"---- pattern unmatched ----"<<endl;
To my surprise, the it printed out pattern unmatched. If I change str to "banan(an)a", the result is pattern matched. Feels like boost.Regex doesn't treat ( ) as subexpression. Any idea?
You're escaping the parentheses, so Boost.Regex, treats them as literal "(" and ")" instead of special characters. The regex will match strings like "banan(an)))))a" In Christ, Steven Watanabe
Go you. Thanks. Qihong On Tue, Mar 17, 2009 at 10:43 PM, Steven Watanabe <watanabesj@gmail.com>wrote:
AMDG
Qihong Wang wrote:
I'm a new boost and regex user. I tried a c++ regex sample as follows
regex pattern("banan\\(an\\)*a"); string str = "bananana";
if(regex_match(str, pattern)) cout<<"---- pattern matched ----"<<endl; else cout<<"---- pattern unmatched ----"<<endl;
To my surprise, the it printed out pattern unmatched. If I change str to "banan(an)a", the result is pattern matched. Feels like boost.Regex doesn't treat ( ) as subexpression. Any idea?
You're escaping the parentheses, so Boost.Regex, treats them as literal "(" and ")" instead of special characters. The regex will match strings like "banan(an)))))a"
In Christ, Steven Watanabe
_______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
Steve, I have another question about this. In boost document about Posix basic regular expression syntax, a section beginning \( and ending \) is defined as a marked sub-expression. In Posix Extended Regular Expression Syntax, A section beginning ( and ending ) is defined as a marked sub-expression. May I say regex class or regex_match support ERE instead of BRE by default? Thanks, Qihong On Tue, Mar 17, 2009 at 10:43 PM, Steven Watanabe <watanabesj@gmail.com>wrote:
AMDG
Qihong Wang wrote:
I'm a new boost and regex user. I tried a c++ regex sample as follows
regex pattern("banan\\(an\\)*a"); string str = "bananana";
if(regex_match(str, pattern)) cout<<"---- pattern matched ----"<<endl; else cout<<"---- pattern unmatched ----"<<endl;
To my surprise, the it printed out pattern unmatched. If I change str to "banan(an)a", the result is pattern matched. Feels like boost.Regex doesn't treat ( ) as subexpression. Any idea?
You're escaping the parentheses, so Boost.Regex, treats them as literal "(" and ")" instead of special characters. The regex will match strings like "banan(an)))))a"
In Christ, Steven Watanabe
_______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
AMDG Qihong Wang wrote:
I have another question about this. In boost document about Posix basic regular expression syntax, a section beginning \( and ending \) is defined as a marked sub-expression. In Posix Extended Regular Expression Syntax, A section beginning ( and ending ) is defined as a marked sub-expression. May I say regex class or regex_match support ERE instead of BRE by default?
Actually, the default is perl. In Christ, Steven Watanabe
participants (2)
-
Qihong Wang -
Steven Watanabe