c++,regex,c++11 , How to match one of multiple alternative patterns with C++11 regex [duplicate]


How to match one of multiple alternative patterns with C++11 regex [duplicate]

Question:

Tag: c++,regex,c++11

This question already has an answer here:

With Perl, the following results in a match:

echo xyz | perl -ne 'print if (/.*(yes|no|xy).*/);'

I'm trying to achieve the same thing with a C++ regex. The ECMAScript syntax documentation says

A regular expression can contain multiple alternative patterns simply by separating them with the separator operator (|): The regular expression will match if any of the alternatives match, and as soon as one does.

However, the following example seems to suggest that std::regex_match only matches the first two alternatives, ignoring the third:

std::string pattern1 = ".*(yes|no|xy).*";
std::string pattern2 = ".*(yes|xy|no).*";
std::regex re1(pattern1);
std::regex re2(pattern2);
for (std::string str : {"yesplease", "bayes", "nobody", "anode", "xyz", "abc"} ) {
   if (std::regex_match(str,re1)) {
       std::cout << str << "\t\tmatches " << pattern1 << "\n";
   }
   else if (std::regex_match(str,re2)) {
       std::cout << str << "\t\tmatches " << pattern2 << "\n";
   }
}

Output:

yesplease   matches .*(yes|no|xy).*
bayes       matches .*(yes|no|xy).*
nobody      matches .*(yes|no|xy).*
anode       matches .*(yes|no|xy).*
xyz         matches .*(yes|xy|no).*

How can I obtain the same behaviour as with my Perl regex example, i.e. having 'xyz' match pattern1?


Answer:

It looks like regex is not fully implemented in gcc version 4.8.2 but rather in later versions of gcc (i.e., version > 4.9.0).

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53631

In gcc version 4.9.0 works ok LIVE DEMO

So I guess you'll have to upgrade to newer version of gcc.


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