boost regex expression

Boost.Regex provides three different functions to search for regular expressions

1. regex_match

#include <boost/regex.hpp>
#include <string>
#include <iostream>

int main() {
  std::string s = "Boost Libraries";
  boost::regex expr("\\w+\\s\\w+");
  std::cout << std::boolalpha << boost::regex_match(s, expr) << std::endl;
  return ;
}

boost::regex_match() compares a string with a regular expression. It will return true only if the expression matches the complete string.

2. regex_search

#include <boost/regex.hpp>
#include <string>
#include <iostream>

int main() {
  std::string s = "Boost Libraries";
  boost::regex expr("(\\w+)\\s(\\w+)");
  boost::smatch what;
  if (boost::regex_search(s, what, expr)) {
    std::cout << what[] << std::endl;
    std::cout << what[] << "_" << what[] << std::endl;
  }
  return ;
}

3. regex_replace

#include <boost/regex.hpp>
#include <string>
#include <iostream>

int main() {
  std::string s = " Boost Libraries";
  boost::regex expr("\\s");
  std::string fmt("_");
  std::cout << boost::regex_replace(s, expr, fmt) << std::endl;
  return ;
}

4. boost xpressive

Like boost regex, boost xpressive provides functions to search strings using regular expressions. However, boost xpressive makes it possible to write down regular expressions as C++ code rather than strings. That makes it possible to check at compile time whether a regular expression is valid or not.

#include <boost/xpressive/xpressive.hpp>
#include <string>
#include <iostream>

using namespace boost::xpressive;

int main() {
  std::string s = "Boost Libraries";
  sregex expr = sregex::compile("\\w+\\s\\w+");
  std::cout << std::boolalpha << regex_match(s, expr) << std::endl;
  return ;
}

boost::xpressive::regex_match() compares strings, boost::xpressive::regex_search() searches in strings, and boost::xpressive::regex_replace() replaces characters in strings. The type of regular expression in boost xpressive depends on the type of string being searched. Because s is based on std::string, the type of the regular expression must be boost::xpressive::sregex.

#include <boost/xpressive/xpressive.hpp>
#include <iostream>

using namespace boost::xpressive;

int main() {
   const char* c = "Boost Libraries";
   cregex expr = cregex::compile("\\w+\\s\\w+");
   std::cout << std::boolalpha << regex_match(c, expr) << std::endl;
   return ;
}

For strings of type const char*, use the class boost::xpressive::cregex.