Re: [Boost-bugs] [Boost C++ Libraries] #4716: boost::filesystem::path operator>> drops leading slash.

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #4716: boost::filesystem::path operator>> drops leading slash.
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-10-19 19:02:11

#4716: boost::filesystem::path operator>> drops leading slash.
--------------------------------------+-------------------------------------
  Reporter:  norman.wilson@…          |       Owner:         
      Type:  Bugs                     |      Status:  new    
 Milestone:  To Be Determined         |   Component:  None   
   Version:  Boost 1.44.0             |    Severity:  Problem
Resolution:                           |    Keywords:         
--------------------------------------+-------------------------------------

Comment (by luke@…):

 I ran into this same issue.  However, I think its actually worse than
 dropping the leading slash.  It drops the leading character whatever it is
 unless it is a double quote.

 boost\filesystem\v3\path.hpp

 template <class Char, class Traits>
 inline std::basic_istream<Char, Traits>&
 operator>>(std::basic_istream<Char, Traits>& is, path& p)
 {
   std::basic_string<Char> str;
   is >> boost::io::quoted(str, static_cast<Char>('&'));
   p = str;
   return is;
 }

 The problem is coming from the boost::io::quoted function.

 boost\io\detail\quoted_manip.hpp

 //  extractor for non-const std::basic_string& proxies
 template <class Char, class Traits, class Alloc>
 std::basic_istream<Char, Traits>& operator>>(std::basic_istream<Char,
 Traits>& is,
   const quoted_proxy<std::basic_string<Char, Traits, Alloc>&, Char>&
 proxy)
       {
         Char c;
         is >> c;
         if (c != proxy.delim)
         {
           proxy.string = c;
           is >> proxy.string;
           return is;
         }
         proxy.string.clear();
         {
           boost::io::ios_flags_saver ifs(is);
           is >> std::noskipws;
           for (;;)
           {
             is >> c;
             if (!is.good())  // cope with I/O errors or end-of-file
               break;
             if (c == proxy.escape)
             {
               is >> c;
               if (!is.good())  // cope with I/O errors or end-of-file
                 break;
             }
             else if (c == proxy.delim)
               break;
             proxy.string += c;
           }
         }
         return is;
       }

 The function is checking if the first character in the stream is a double
 quote, if it is all works fine.  However if its not it assigns the value
 of the first character to the proxy.string and then uses the insertion
 operator to get the rest of the characters.  However the insertion is not
 an append it is an assignment so the effect is the first character is
 lost.  I'm not exactly sure if this is expected behavior of this function
 of not.  A workaround is to change the proxy.string = c; to is.unget();
 This will preserve the first character.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/4716#comment:1>
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