Delivery-Date: Thu Sep  4 10:23:25 2008
Message-Id: <200809041721.m84HLSBb008625@bourbon.usc.edu>
To: cs551@merlot.usc.edu
Subject: Re: CSCI 551- Question in warm up project 1
Date: Thu, 04 Sep 2008 10:21:28 -0700
From: Bill Cheng <william@bourbon.usc.edu>

Someone wrote:

  > I had issue with  packet construction. Could you please help me out ?
  > 
  > I had used a structure to hold the  different packet fields i.e. message
  > type, offset, data length, and the data.
  > 
  > While sending using sockets, I used to use a pointer to the structure
  > variable to send the entire packet. Is it fine, if I do it this way ?

If you do it very carefully, it should be okay!

  > Or should i always do it, by packing all the fields into a string and then
  > send using the pointer to the string ?

I would prefer this 2nd approach for the header.  This way,
you can verify what's in the buffer before you start sending.
Please use the debugger to verify the content of your buffer.

I've just modified the beginning of my Sockets Programming 
slides:

    http://merlot.usc.edu/cs551-f08/lectures/tentative/01a_sockets.pdf

On page 4, I've added a new command I've recently learned in
gdb:

    printf "%02x\n",buf[0]

If you use the "print" command in gdb, it will print out an
integer value.  You should use the "printf" command in gdb
to display a byte in hex like I've done above.

By the way, I'm a bit worried when you used the word "string"!
If you really think of this character buffer as a string, you
may use functions that operate on string to manipulate data
in this buffer.  Sometimes this would work, and sometimes not.
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>