Programmer 7500/MAX_PROGRAMMERS.iso/INFO/TURBOPAS/MODIFY.ZIP/MODIFY.PAS

Pascal/Delphi Source File | 1988-02-20 | 3.7 KB | 70 lines

PROGRAM modify4;
  {  Version B, 12/23/87.  Minor bug fixes, additional comments added
  regarding how to deal with headers which fall across the boundaries
  of your search buffer.}

  {  This is an update of Modify 1.00, which is designed to
  allowing quick cloning under Turbo version 3.  This now
  works under version 4.  Address questions and bug reports
  to Bob Tolz, Compuserve ID #70475,1071.  Original comments for
  the modify version 1.00 follow.  Please read them with a grain
  of salt, given the changes required for upgrading to 4.0}

  {----------  Begin Modify 1.00 Comments ------------}
  {  PROGRAM Modify_Turbo_COM_File; }
  {  For DOS versions of Turbo only }

  (*
  Purpose of Modify:
  Like the popular CLONE.PAS and CLOVER.PAS, Modify provides a method
  by which Turbo programmers can allow users to create customized versions
  of their programs without recompiling the source.

  How it works:
  Modify takes advantage of the fact that Turbo stores typed constants
  in the code segment.  This means that the location of a given typed
  constant in a .COM file will always correspond to its offset from CSeg, less
  the size of the Program Segment Prefix ($100 bytes).  An integer variable
  (typed constant) located at CSeg:$0500 while a program is in memory, for
  example, can be found by Seek-ing to the 1024th byte (1024 = $400) in the
  .COM file.  If you were then to write the current value of the integer
  variable to disk, the current value would become the default or initial
  value.  This is what Modify does, essentially, except that it can change
  multiple variables in one swoop.

  How to use the Modify function:
  The demonstration program included here shows how to use Modify, but
  I'll explain the procedure briefly anyway:
  First, declare all the variables that you want to be able to modify
  as typed constants (global) in a single cluster.  The cluster should
  begin with a "header string", probably the name of the program and perhaps
  a version number as well.  This will help Modify insure that the .COM
  file being modified is the right one.  (Be sure that the header string is
  unique--if you release an updated version of your Modify-able program,
  you should change the header string.)  The end of the cluster should be
  marked by a one-byte dummy variable, such as "Tail" in the demo program.
  In between you can put as many variables as you wish.
  Modifying your program is then simple: just call the Modify function
  with three parameters: the name of the .COM file, the header string, and
  the dummy variable used to mark the end of the cluster.  Modify takes
  care of everything else, and returns an error code to indicate what
  happened.  (See the list of return codes, below.)

  Modify lacks some of the features of CLONE and CLOVER--it can't make
  backup versions of programs, for example--and it is slightly riskier
  (in my own programs, I ask the user to confirm that he has a backup
  copy of the program before calling Modify).  But it is the smallest,
  fastest, and simplest routine to clone COM files that I've seen, and
  I think that many people will find that its advantages more than
  compensate for its disadvantages.  (I almost forgot: Modify, like
  Clover, works fine for programs with overlays.  It will not, however,
  work with EXE files created by Turbo Extender.  Randy Forgaard is
  reportedly working on a simlar routine that will.)

  Special thanks to Randy Forgaard for his suggestions, as well as to Bob
  Tolz, Bela Lubkin, and James Troutman.  Please address all comments,
  suggestions, etc. to:
  Brian Foley, CompuServe ID #76317,3247.
  *)
  {----------  End Modify 1.00 Comments ------------}