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

From: Shams (shams_at_[hidden])
Date: 2007-03-29 09:30:00

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_at_[hidden]>
Newsgroups: gmane.comp.lib.boost.user
To: <boost-users_at_[hidden]>
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.