• read, write, close
• This is not as complex
• close
  • int close(int fd);
  • Can fail, but what do you do if it does?
    • man 2 close warns that it is a serious programming error not to check the results of a close.
  • Frees the file descriptor.
  • There are problems that can occur on NFS mounted file systems.
  • If this is the last reference to the file, it will be removed.
  • Close does not sync the file, it may be buffered,
    • use int fsync(int fd); to sync the buffer.
    • Or non-buffered files, we will discuss later.
• read/write
  • ssize_t read(int fd, void *buf, size_t count);
  • ssize_t write(int fd, const void *buf, size_t count);
  • Perform raw i/o
  • Given a buffer, attempt to read/write that many bytes
  • Returns
    • -1 on error
    • the number of bytes read or written.
  • There is the possibility of a partial read/write problem
• lseek: Move around in a file
  • off_t lseek(int fd, off_t offset, int whence);
    • fd is a valid file descriptor
    • offset is the size in bytes to move.
    • whence where to move
      • SEEK_SET : set the file offset to a position
        • Negative is not acceptable
        • You can seek past the end of a file, this is ok.
      • SEEK_CUR: the current location + the offset
        • This can include a negative offset
        • But you can not seek before the start of a file.
      • SEEK_END
        • End of the file plus offset
        • This is one past the end if offset = 0.
    • The return value is the position (in bytes) in the file.
    • Writing past the end of the file can create a hole.
      • This is not a bug but a feature.
      • You can write into holes.
      • If you read data from a hole, the value is 0.
      • look at hole.C
      • look at
• Look at seeker.C in some detail