/** @file list5703.cpp */
/** Listing 57-3. Expanding Variables */
std::map<std::string, std::string> variables;

std::string expand(std::string str)
{
   std::string::size_type start(0); // start searching here
   while (true)
   {
      // Find a dollar sign.
      std::string::size_type pos(str.find('$', start));
      if (pos == std::string::npos)
         // No more dollar signs.
         return str;
      if (pos == str.size() - 1 or str[pos + 1] != '(')
         // Not a variable reference. Skip the dollar sign,
         // and keep searching.
         start = pos + 1;
      else
      {
         std::string::size_type end(str.find(')', pos));
         if (end == std::string::npos)
            // No closing parenthesis.
            return str;

         // Get the variable name.
         std::string varname(str.substr(pos + 2, end - pos - 2));
         // Replace the entire variable reference.
         str.replace(pos, end - pos + 1, variables[varname]);
         // Scan the replacement text for more variables.
         start = pos;
      }
   }
}