RE: [Boost-Users] Re: [crc] Simple example please

From: Alex Henderson (Alex.Henderson_at_[hidden])
Date: 2003-06-11 11:19:24

Having tried your example code I also get 'readsome' returning zero. That's
with BCB5 (Rogue Wave's STL). However, reading the whole file into a char
array works fine with crc::process_bytes.

Really I only needed an example of handling the crc part. The file IO part I
can do in many different ways.

I really know nothing of CRC, only that it's useful and complicated in equal
measure. Thanks for creating the library and for donating it to boost!

Alex

> -----Original Message-----
> From: Daryle Walker [mailto:darylew_at_[hidden]]
> Sent: 11 June 2003 02:24
> To: Boost-Users_at_[hidden]
> Subject: [Boost-Users] Re: [crc] Simple example please
>
>
> On Tuesday, June 10, 2003, at 9:08 AM, Vladimir Prus wrote:
>
> [SNIP]
> > Here's the function that I use for the same purpose. Might not be
> > optimal, but works:
> >
> > unsigned file_crc(const string& name)
> > {
> > #if defined(__GNUC__) && __GNUC__ < 3
> >     ifstream ifs(name.c_str(), ios::binary);
> > #else
> >     ifstream ifs(name.c_str(), ios_base::binary);
> > #endif
> >     if (!ifs)
> >         return 0;
> >     else {
> >         using namespace boost;
> >
> >         crc_32_type crc32;
> >         int c;
> >         while( (c = ifs.rdbuf()->sbumpc()) != -1)
> >              crc32.process_byte(char(c));
> >         return crc32.checksum();
> >     }
> > }
> >
> >
> > I believe some example of this kind should be included... Daryle, what
> > do you think?
>
> I'll consider it.
>
> [A few hours pass...]
>
> How about something like this:
>
> //================================================================
> #include <cstdlib>
> #include <exception>
> #include <fstream>
> #include <ios>
> #include <iostream>
> #include <ostream>
>
> #include <boost/crc.hpp>
>
>
> #ifndef BLOCK_SIZE
> #define BLOCK_SIZE  1024
> #endif
>
>
> int
> main
> (
>      int           argc,
>      char const *  argv[]
> )
> try
> {
>      boost::crc_32_type  result;
>
>      // Loop over each file argument
>      for ( int i = 1 ; i < argc ; ++i )
>      {
>          std::ifstream  ifs( argv[i], std::ios_base::binary );
>          if ( ifs/*std::ifstream ifs(argv[i],
> 		 std::ios_base::binary)*/ )
>          {
>              /*char             buffer[ BLOCK_SIZE ];
>              std::streamsize  len;
>
>              while ( 0 < (len = ifs.readsome( buffer, BLOCK_SIZE )) )
>              {
>                  result.process_bytes( buffer, len );
>              }*/
>              char c;
>              while ( ifs.get(c) )
>              {
>                  result.process_byte( c );
>              }
>          }
>          else
>          {
>              std::cerr << "Failed to open file '" << argv[i]
> 			 << "'." << std::endl;
>          }
>      }
>
>      std::cout << std::hex << result.checksum() << std::endl;
>      return EXIT_SUCCESS;
> }
> catch ( std::exception &e )
> {
>      std::cerr << "Found an exception with '" << e.what()
> 	 << "'." << std::endl;
>      return EXIT_FAILURE;
> }
> catch ( ... )
> {
>      std::cerr << "Found an unknown exception." << std::endl;
>      return EXIT_FAILURE;
> }
> //================================================================
>
> Note in the "if" statement, I had the construction in it.  However,
> neither one of my compilers took it!  Moving the constructor call
> worked, but I thought my original method should be accepted.
>
> One compiler finished after the above 'fix'.  The other (a variant of
> GCC 3.1) complained about missing symbols at link-time; it could not
> create the global objects hidden in Boost.CRC.  (I haven't worked on
> the code in a long time; there could be quirks on compilers written
> after Boost.CRC.)
>
> When I ran the program under the compiler that worked, the "readsome"
> function always returned zero!  There were no suitable substitutes; the
> "read" function doesn't tell you how many characters it read (bad if
> the last block isn't full) and the multi-character "get" functions use
> delimiters.  So this program is stuck at single-character reads at the
> moment.  Maybe I should switch to the stream-buffer method you used.
>
> Can you try this out to make sure the problems aren't just mine?
>
> Daryle
>
>
>
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