Vladimir Pozdyayev wrote:
some of my algorithms' calculations have to be performed directly on the expression tree, the compiled state machine won't help. Is it possible to restore the tree from the information provided by the library? That is, given the regex "((?:a|b)*?)(b+)", end up with an object like
new cat( new match( new kleene_lazy( new alt( new charset( "a" ), new charset( "b" ) ) ) ), new match( new repeat( new charset( "b" ) ) ) )
FYI, xpressive builds such a parse tree (see http://boost-sandbox.sf.net/libs/xpressive). And xpressive's compile-time design allows for multiple back-ends (NFA, backtracking NFA, DFA) without paying for ones that aren't used. However, xpressive is hard-coded to use a backtracking NFA for now, and there is no clean interface for plugging in a different back-end. It is also not as mature or as widely used as Boost.Regex. Feel free to contact me offline if you want more information.
And now for something completely different.
The following program outputs ' aa', where the first char is \0. If we replace <smatch> by <cmatch>, the output is ok. That holds for the regex5 as well as the regex library in boost 1.31.0. Am I missing something? (MSVC 7.0)
#include <boost/regex.hpp> #include <iostream> main() { boost::smatch m; boost::regex_match( "aaa", m, boost::regex( ".*" ) ); std::cout << m[ 0 ] << "\n"; }
I think there are 2 overloads of the regex_match algorithm coming into play here. They are: bool regex_match( std::string const &, smatch &, regex const & ); bool regex_match( char const *, cmatch &, regex const & ); When you pass a smatch, the first overload is getting chosen, so the string literal is converted into a std::string temporary, which gets destroyed when the regex_match algorithm returns. That leaves the smatch object holding invalid iterators, which is why you are seeing garbage. When you pass a cmatch, the second overload is getting chosen, and no temporary string object is created -- the cmatch object will hold pointers into the string literal. HTH -- Eric Niebler Boost Consulting www.boost-consulting.com