Re: [Boost-users] boost::format with empty string...

29 Mar 2007

      Hi,

I assume you're using the current official release.
I believe the problem is already fixed in 1.34 in CVS.

Thanks
Shams

----- Original Message ----- 
From: "Early Ehlinger" <early@respower.com>
Newsgroups: gmane.comp.lib.boost.user
To: <boost-users@lists.boost.org>
Sent: Thursday, March 29, 2007 4:46 AM
Subject: boost::format with empty string...
...
Using MS Visual C++ 2005, Express Edition, the following snippet causes an 
assertion failure due to a NULL pointer in the bowels of boost::format:
boost::format f( "test %1%\n" );
 f % "";
I traced it down to boost/format/feed_args.hpp:
template<class Ch, class Tr, class Alloc>
   void mk_str( std::basic_string<Ch,Tr, Alloc> & res,
                const Ch * beg,
                typename std::basic_string<Ch,Tr,Alloc>::size_type size,
                std::streamsize w,
                const Ch fill_char,
                std::ios_base::fmtflags f,
                const Ch prefix_space, // 0 if no space-padding
                bool center)
   // applies centered/left/right  padding  to the string  [beg, beg+size[
   // Effects : the result is placed in res.
   {
       typedef typename std::basic_string<Ch,Tr,Alloc>::size_type 
size_type;
       res.resize(0);
       if( ( w<=0 || static_cast<size_type>(w) <=size)) {
           // no need to pad.
           res.reserve(size + !!prefix_space);
           if(prefix_space)
             res.append(1, prefix_space);
           res.append(beg, size); <<--- crashes, because beg==NULL and 
size==0
...
My suggested fix looks like this:
   template<class Ch, class Tr, class Alloc>
   void mk_str( std::basic_string<Ch,Tr, Alloc> & res,
                const Ch * beg,
                typename std::basic_string<Ch,Tr,Alloc>::size_type size,
                std::streamsize w,
                const Ch fill_char,
                std::ios_base::fmtflags f,
                const Ch prefix_space, // 0 if no space-padding
                bool center)
   // applies centered/left/right  padding  to the string  [beg, beg+size[
   // Effects : the result is placed in res.
   {
       typedef typename std::basic_string<Ch,Tr,Alloc>::size_type 
size_type;
       res.resize(0);
       if(size && ( w<=0 || static_cast<size_type>(w) <=size)) {
           // no need to pad.
           res.reserve(size + !!prefix_space);
           if(prefix_space)
             res.append(1, prefix_space);
           res.append(beg, size);
       }
       else {
           std::streamsize 
n=static_cast<std::streamsize>(w-size-!!prefix_space);
           std::streamsize n_after = 0, n_before = 0;
           res.reserve(w); // allocate once for the 2 inserts
           if(center)
               n_after = n/2, n_before = n - n_after;
           else
               if(f & std::ios_base::left)
                   n_after = n;
               else
                   n_before = n;
           // now make the res string :
           if(n_before) res.append(n_before, fill_char);
           if(prefix_space)
             res.append(1, prefix_space);
           if ( size )
             res.append(beg, size);
           if(n_after) res.append(n_after, fill_char);
       }
   } // -mk_str(..)
-- Early Ehlinger, President, ResPower, Inc.