Objective

You'll need two files for this lab:

http://www.cs.wpi.edu/~jburge/courses/c02/cs2011/labs/lab4.asm

and

http://www.cs.wpi.edu/~jburge/courses/c02/cs2011/labs/LAB4FILE.TXT

Download these on to your floppy disk using a web browser. There are links to them on the course home page.

This program will not assemble.  You'll need to edit it and add some assembly code where indicated by **. When completed, the program will open an existing file, read data from it, ask you for a new file name, read the name using buffered I/O, open the new file, write the data read earlier into it, and close both files.  You'll need to refer to Irvine when doing this.

Use the debugger to test this out and keep an eye on the registers after each INT 21 instruction. If the carry flag is set, you can look at the error code to see what went wrong (where's the error code?  look in Irvine!).

After your program is working, answer the following questions:

• type the contents of the file you just created ("type filename"). What does it say? __________________________________________________________
  
  
• does it match the input file (LAB4FILE.TXT). If not, you'll need to see what went wrong!
  __________________________________________________________
  
  
• what did the code have to do in order to move 0 into the location pointed to by BX?
  
  
• Why couldn't you just initialize the input buffer to zero when reading in the name and skip the part where you add a zero on to the end of the string? ______________________________
  
  
•  This program would not be acceptable as anything other than some test code to play with DOS I/O instructions.  What would you need to add to it to make this code more robust and to protect your existing data (a general answer is fine, you don't have to give the code needed to implement it!).

You will need to turn in this handout at the end of your lab session to receive credit for the lab.