irstlm/src/gzfilebuf.h

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// $Id: gzfilebuf.h 236 2009-02-03 13:25:19Z nicolabertoldi $

#ifndef _GZFILEBUF_H_
#define _GZFILEBUF_H_

#include <streambuf>
#include <cstring> 
#include <zlib.h>

class gzfilebuf : public std::streambuf {
public:
  gzfilebuf(const char *filename)
  { _gzf = gzopen(filename, "rb"); 
    setg (_buff+sizeof(int),     // beginning of putback area
          _buff+sizeof(int),     // read position
          _buff+sizeof(int));    // end position
  }
  ~gzfilebuf() { gzclose(_gzf); }
protected:
  virtual int_type overflow (int_type c) {
      throw;
  }

  // write multiple characters
  virtual
  std::streamsize xsputn (const char* s,
                          std::streamsize num) {
      throw;
  }

  virtual std::streampos seekpos ( std::streampos sp, std::ios_base::openmode which = std::ios_base::in | std::ios_base::out ){ throw;
  }

  //read one character
  virtual int_type underflow () {
    // is read position before end of _buff?
        if (gptr() < egptr()) {
            return traits_type::to_int_type(*gptr());
        }

        /* process size of putback area
         * - use number of characters read
         * - but at most four
         */
        unsigned int numPutback = gptr() - eback();
        if (numPutback > sizeof(int)) {
            numPutback = sizeof(int);
        }

        /* copy up to four characters previously read into
         * the putback _buff (area of first four characters)
         */
        std::memmove (_buff+(sizeof(int)-numPutback), gptr()-numPutback,
                      numPutback);

        // read new characters
        int num = gzread(_gzf, _buff+sizeof(int), _buffsize-sizeof(int));
        if (num <= 0) {
            // ERROR or EOF
            return EOF;
        }

        // reset _buff pointers
        setg (_buff+(sizeof(int)-numPutback),   // beginning of putback area
              _buff+sizeof(int),                // read position
              _buff+sizeof(int)+num);           // end of buffer

        // return next character
        return traits_type::to_int_type(*gptr());
  }

  std::streamsize xsgetn (char* s,
                          std::streamsize num) {
    return gzread(_gzf,s,num);
  }

private:
  gzFile _gzf;
  static const unsigned int _buffsize = 1024;
  char _buff[_buffsize];
};

#endif

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