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

4 Mar 2005


      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;
        }
    }
};

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;
        }
    }
};