Question

why does the following boost regex not return the results I am looking for (starts with 0 ore more whitespace followed by one or more asterisk)?

boost::regex tmpCommentRegex("(^\\s*)\\*+");

for (std::vector<std::string>::iterator vect_it =
    tmpInputStringLines.begin(); vect_it != tmpInputStringLines.end();
    ++vect_it) {

    boost::match_results<std::string::const_iterator> tmpMatch;
    if (boost::regex_match((*vect_it), tmpMatch, tmpCommentRegex,
        boost::match_default) == 0) {

        std::cout << "Found comment " << (*vect_it) << std::endl;
    } else {
        std::cout << "No comment" << std::endl;
    }
}

On the following input:

* Script 7
[P]%OMO      * change
[P]%QMS      * change
[T]%OMO      * change
[T]%QMM      * change
[S]%G1       * Resume
[]

This should read

Found comment * Script 7
No comment
No comment 
No comment 
No comment 
No comment 
No comment 

Answer 1

Quoting from the documentation for regex_match:

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.

None of your input lines are matched by your regular expression as a whole, so the program works as expected. You should use regex_search to get the desired behavior.

Besides, regex_match and regex_search both return bool and not int, so testing for == 0 is wrong.