Answering Robert's Question

• What will this do?

  • ofstream oFile;
    oFile.open(...);
    oFile  << "1234" << 7 ;
        

  • Look at cfile.C
  • And the outputFile
  • What is in this file?
  • What happens when we do I/O to a standard output file stream in C++?
• What will this do, assuming fd is a valid file descriptor?

• write(fd,"1234",4);
      

• How about this?

• int x  = 7;
  write(fd, &x,sizeof(int));
      

• Both will write 4 bytes to a file, one in ascii, the other in binary
  • That is really silly, both are in binary!
  • But this first will write the binary for the ascii characters "1", "2", "3" and "4"
  • While the second will write the (4 byte) bit pattern for the number 7.
• See code/iodemo.C for this and more...
• But what is in the file?
• See code/xd.c for more information
  • There is actually a pair of system programs that do this
  • od and hexdump.
  • But they play around with byte order and I could write it anyway.
  • Remember, (or know) that the intel chip is little endian
    • 
    • The small part, or little end, of the number is put first in the word.
    • This is not the only way that bytes are ordered in a word.