[boost] Re: Re: Re: [iostreams]Majorinteracechangesplanned--commentsrequested

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2005-03-04 13:16:40

Peter Dimov wrote:
> Peter Dimov wrote:
>
>> Time for a contest. "Write the best non-blocking comment skipping
>> filter". :-)
>
> Here's my entry.
>
> struct filter
> {
>     char comment_char_;
>     bool in_comment_;
>
>     filter(): comment_char_( '#' ), in_comment_( false )
>     {
>     }
>
>     template< class Source > int get( Source & src )
>     {
>         int c;
>
>         for( ;; )
>         {
>             if( in_comment_ )
>             {
>                 for( ;; )
>                 {
>                     c = src.get();
>
>                     if( c == eof || c == eagain ) return c;
>                     if( c == '\n' ) break;
>                 }
>
>                 in_comment_ = false;
>             }
>
>             c = src.get();
>
>             if( c != comment_char_ ) return c;
>
>             in_comment_ = true;
>         }
>     }
> };

This one is simple enough to put in the tutorial.

> struct filter2
> {
>     char comment_char_;
>     bool in_comment_;
>
>     filter2(): comment_char_( '#' ), in_comment_( false )
>     {
>     }
>
>     template< class Source > int read( Source & src, char * s, int n )
>     {
>         int m = src.read( s, n );
>
>         if( m <= 0 ) return m;
>
>         int r = 0; // dest: [s, s + r)
>
>         char const * p = s; // src: [p, p + m)
>
>         for( ;; )
>         {
>             if( in_comment_ )
>             {
>                 char const * q = static_cast<char const *>( memchr(
> p, '\n', m ) );
>
>                 if( q == 0 )
>                 {
>                     return r;
>                 }
>
>                 m -= q - p + 1;
>                 p = q + 1;
>                 in_comment_ = false;
>             }
>
>             char const * q = static_cast<char const *>( memchr( p,
> comment_char_, m ) );
>
>             if( q == 0 )
>             {
>                 memmove( s + r, p, m );
>                 return r + m;
>             }
>
>             memmove( s + r, p, q - p );
>             r += q - p;
>             m -= q - p + 1;
>             p = q + 1;
>             in_comment_ = true;
>         }
>     }
> };

Pretty sneaky! Try that with a tab-expanding filter ;-)

Jonathan