C++ Question
Why doesn't boost regex '.{2}' match '??'
I'm trying to match some chunks if interesting data within a data stream.
There should be a leading
<??>If the last two characters are alphanumeric, the following code works as expected. If they're
??// Set up a pre-populated data buffer as an example
std::string haystack = "Fli<data??>bble";
// Set up the regex
static const boost::regex e("<\\w{4}.{2}>");
std::string::const_iterator start, end;
start = haystack.begin();
end = haystack.end();
boost::match_flag_type flags = boost::match_default;
// Try and find something of interest in the buffer
boost::match_results<std::string::const_iterator> what;
bool succeeded = regex_search(start, end, what, e, flags); // <-- returns false
I've not spotted anything in the documentation which suggests this should be the case (all but NULL and newline should be match AIUI).
So what have I missed?
Answer Source
Because ??> is a trigraph, it will be converted to }, Your code is equivalence with:
// Set up a pre-populated data buffer as an example
std::string haystack = "Fli<data}bble";
// Set up the regex
static const boost::regex e("<\\w{4}.{2}>");
std::string::const_iterator start, end;
start = haystack.begin();
end = haystack.end();
boost::match_flag_type flags = boost::match_default;
// Try and find something of interest in the buffer
boost::match_results<std::string::const_iterator> what;
bool succeeded = regex_search(start, end, what, e, flags); // <-- returns false
You can change to this, note: I use std::regex which is likely the same:
std::string haystack = "Fli<data?" "?>bble";