June 19

• How does input and output work for -W?

  Input is through input redirection. Output is through output redirection. Thus, read from standard input and write to standard output.

June 5

• How can I test?

  The hexdump is modelled after xxd. Try using xxd. Read the man pages for it too.

• What corrections have been made?

  When the file is to be read from the command line, instead of standard input, it will always have a -i option. For a small amount of extra credit, you can assume that a name that sits by itself is the name of a file (as it was originally posted).

• In byteToHex, you pass the parameter as char. This can cause problems when I convert to an int because it appears as negative. What should I do?.

  Think of a char as a one byte int. int's can either be signed or unsigned. While it's not specified whether char should be signed or unsigned, it's considered signed.

  Thus, when you convert it to an int it may cause the value to stay negative.

  For purposes of converting to hex, it's usually easier to do the following:

  void byteToHex( char byte, char * hexArray ) 
  {
     unsigned char byte2 = byte ; // Save as unsigned
  }
  

  that way casting byte2 to an unsigned int works the way you expect it to.

• Can command line switches be combined?

  These are valid/invalid combinations:

  • -p and -a will not appear together (although you could just pick one arbitarily).

  • Any subset of the following options can occur: -p,

    -i, -o and -w (in any order).

  • Any subset of the following options can occur: -a,

    -i, -o and -w (in any order).

  • Options won't be combined together into a single switch, (as in -pi).
  • You should print out errors for unknown switches in the order processed, but otherwise ignore them. For example: if the input where

    hexdump -z -ma -p -i foo.name
    

    you should output:

    Unknown switch: -z
    Unknown switch: -ma
    
    00 00 00 00 00 00 01 00 2E 64 79 6E 73 79 6D 00
    2E 72 65 6C 2E 64 79 6E
    
    Total bytes: 24
    

    Many UNIX utilities tend to abort when there are unknown switches, so this is somewhat non-standard behavior to ignore unknown switches. The error messages are printed just so we can tell they are there.
  Note that:
  • Switches are case sensitive. That is, -p and -P are not the same switch.
  • You can assume that a valid switch will have the correct number of arguments. Thus, you won't have -i or -w with an argument. The argument appears with at least one space after the switch, so you WON'T have -imyinput.file (that could be treated like an invalid switch).
  • When -o is used, print the error message to the file as well. Again, this is not standard (error messages are typically printed to standard error, not a file). However, it does make printing to a file equivalent to printing to the screen.

  If you can, try to avoid too much code duplication. In particular, there are nice ways to parameterize whether you are printing to a file or to standard output.

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