如何使用Boost正则表达式检测字符串中的ESC

Question

I need to determine if a file is PCL encoded. So I am looking at the first line to see if it begins with an ESC character. If you know a better way feel free to suggest. Here is my code:

bool pclFlag = false;
if (containStr(jobLine, "^\\e")) {
   pclFlag=true;
}

bool containStr(const string& s, const string& re)
{
   static const boost::regex e(re);
   return regex_match(s, e);
}

pclFlag does not get set to true.

Answer 1

You've declared boost::regex e to be static, which means it will only get initialized the very first time your function is called. If your search here is not the first call, it will be searching for whatever string was passed in the first call.

regex_match must match the entire string. Try adding ".*" (dot star) to the end of your regex.

Important
Note that the result is true only if the expression matches the whole of the input sequence. If you want to search for an expression somewhere within the sequence then use regex_search. If you want to match a prefix of the character string then use regex_search with the flag match_continuous set.
http://www.boost.org/doc/libs/1_51_0/libs/regex/doc/html/boost_regex/ref/regex_match.html

@JoachimPileborg is right... if (jobline[0] == 0x1B) {} is much easier.

Answer 2

Boost.Regex seems like overkill if all you want to do is see if a string starts with a certain character.

bool pclFlag = jobLine.length() > 0 && jobLine[0] == '\033';

You could also use Boost string algorithms:

#include <boost/algorithm/string.hpp>

bool pclFlag = jobLine.starts_with("\033");

If you're looking to see if a string contains an escape anywhere in the string:

bool pclFlag = jobLine.find('\033') != npos;