Boost regex does not match

I made a python regular expression and now I'm supposed to code the program in C++.

I was told to use boost's regex by the respective person.

It is supposed to match a group of at least one to 80 lower alphanumeric characters including underscore followed by a backslash then another group of at least one to 80 lower alphanumeric characters again including an underscore and last but not least a question mark. The total string must be at least 1 character long and is not allowed to exceed 256.

Here is my python regex:

^((?P<grp1>[a-z0-9_]{1,80})/(?P<grp2>[a-z0-9_]{1,80})([?])){1,256}$

My current boost regex is:

^(([a-z0-9_]{1,80})\/([a-z0-9_]{1,80})([?])){1,256}$

Cut down basically my code would look like this:

boost::cmatch match;
bool isMatch;
boost::regex myRegex = "^(([a-z0-9_]{1,80})\/([a-z0-9_]{1,80})([?])){1,256}$";
isMatch = boost::regex_match(str.c_str(), match, myRegex);

Edit: whoops totally forgot the question xDD. My problem is quite simple: The regex doesn't match though it's supposed to.

Example matches would be:

• some/more?
• object/value?
• devel42/version_number?