How can you specify carriage return and newline character match when using boost::regex?
boost, boost-regex, c++, regex
Solution
Try with this one instead :
string str_regex("ATI3\r\nv(\\d+[.]\\d+)\r\nOK\r\n");
Notice that the `\` of `\d` is escaped to become `\\d`.
Applying the same change to your two alternative regular expressions should also make those work.
Explanation :
This is not a problem with the newline or carriage return matching, but rather with escape sequences in string literals. `\d` is not a valid escape sequence for a string literal - in fact my compiler warns me about this :
warning: unknown escape sequence: '\d' [enabled by default]
It is a shortcut for `[:digit:]` recognized by boost::regex. In order for the boost::regex library to 'see' the `\`, it needs to be escaped.
Problem
I am having a problem with `boost::regex` behaviour when it comes to matching `\r` and `\n` characters in a string. I am communicating over a serial port with a modem from my linux C++ application and I am receiving the following message from it ``` ATI3\r\nv3.244\r\nOK\r\n ``` I know that this string is correct as I actually check the ASCII hex values of each character returned. The problem is that my application needs to strip out the version number specified by the `vX.XYZ` part of the string. To this end I am using the following `boost::regex` based code: ``` string str_modem_fw_version_number = ""; string str_regex("ATI3\r\nv(\d+[.]\d+)\r\nOK\r\n"); boost::regex patt; try { patt.assign(str_regex); boost::cmatch what; if (boost::regex_match(str_reply.c_str(), sc_what, patt)) { str_modem_fw_version_number = string(sc_what[1].first,sc_what[1].second); } } catch (const boost::regex_error& e) { cout << e.what() << endl; } ``` The above does not work - I can see the string I get back is correct but I am sure I am making some obvious error with the CR and NL characters in the regex. I have also tried the following which do not work ``` string str_regex("ATI3.*(\d+[.]\d+).*"); string str_regex("ATI3\\r\\nv(\d+[.]\d+)\\r\\nOK\\r\\n"); ``` and variations on a theme but I think I must be missing some basic information on how `boost::regex` treats the NL and CR characters. I have looked through the boost documentation pages without success and so am trying here as a last resort before using an alternative to boost to solve the problem.