Programmer 7500/MAX_PROGRAMMERS.iso/PASCAL/PAS_ALL.ZIP/TI545.ASC

Text File | 1992-02-28 | 7.4 KB | 331 lines

  PRODUCT  :  TURBO PASCAL                           NUMBER  :  545
  VERSION  :  4.0, 5.0, AND 5.5
       OS  :  PC-DOS 3.0 or later, MS-DOS 3.0 or later
     DATE  :  February 28, 1992                        PAGE  :  1/4

    TITLE  :  FILES OPEN EXTEND




  The following is public domain information that has been uploaded
  to  our Forum on CompuServe.  As a courtesy to our users that  do
  not  have  immediate  access  to  CompuServe,  Technical  Support
  distributes these routines free of charge.

  However,  because these routines are public domain programs,  not
  developed by Borland International,  we are unable to provide any
  technical support or assistance using these routines. If you need
  assistance   using   these   routines,    or   are   experiencing
  difficulties,  we  recommend  that you log  onto  CompuServe  and
  request  assistance  from the Forum members that developed  these
  routines.

  The following unit extends the maximum number of  files  that can
  be open simultaneously from 20 to 255.  Files in DOS 2.0 or later
  are  controlled  by  file  handles.   The number of file  handles
  available to application  programs  is  controlled  by  the FILES
  environment  variable  stored  in a CONFIG.SYS file.  If no FILES
  variable  is  established  in a CONFIG.SYS file, then only 8 file
  handles are available.  However,  DOS requires 5 file handles for
  its own use (controlling  devices  such  as  CON, AUX, PRN, etc).
  This le


  aves only 3 handles for use by application programs.

  By specifying a value for the FILES environment variable, you can
  increase the number  of  possible  file  handles from 8 up to 20.
  Since DOS still requires 5, 15 are left for application programs.
  But you cannot normally increase the number of handles beyond 20.

  With DOS version 3.0, a new DOS function was  added  to  increase
  the number of file handles available.  However, the function must
  be called from application programs that have previously reserved
  space for the new file handles.

  The unit EXTEND, described below, resizes the amount of allocated
  memory for a  Turbo  Pascal  program  to allow space for new file
  handles.  In doing so, it also resizes the heap by  adjusting the
  value of FreePtr, the pointer used in FreeList management.  Since
  the  FreeList  is  being manipulated, the heap must be empty when
  the EXTEND unit  is  initialized.    This  can  be  guaranteed by














  PRODUCT  :  TURBO PASCAL                           NUMBER  :  545
  VERSION  :  4.0, 5.0, AND 5.5
       OS  :  PC-DOS 3.0 or later, MS-DOS 3.0 or later
     DATE  :  February 28, 1992                        PAGE  :  2/4

    TITLE  :  FILES OPEN EXTEND




  including EXTEND as one of the first units in your program's USES
  statement.  If any heap has been allocated when EXTEND initialize


  s, the program will halt with an error message.

  Notice  that  the  interface section of the EXTEND unit is empty.
  The initialization section of the unit takes care  of  the unit's
  entire function.  Other than including EXTEND in a program's USES
  statement, no other operation need be preformed.

  Before using EXTEND, you  must  specify  a  FILES variable in the
  CONFIG.SYS file such as the following:

          FILES = 255

  Refer to your DOS User's Guide for more information regarding the
  CONFIG.SYS file and the FILES variable.

  The unit EXTEND is set up for 255 file handles.    You can reduce
  this number by changing the HANDLES constant in the unit's source
  code and  reducing the number specified for the FILES environment
  variable.

  unit Extend;
  {This extends the number of file handles from 20 to 255}
  {DOS requires 5 for itself. Applications can use up to 250}

  interface

  implementation
  uses dos;
  const
          Handles =255;
  {You can reduce the value passed to Handles if fewer files}
  {are required.}

  var
          reg:registers;
  begin
                  {Check the Dos Version}
                  {This technique only works for DOS 3.0 or later}
  reg.ah:=$30;













  PRODUCT  :  TURBO PASCAL                           NUMBER  :  545
  VERSION  :  4.0, 5.0, AND 5.5
       OS  :  PC-DOS 3.0 or later, MS-DOS 3.0 or later
     DATE  :  February 28, 1992                        PAGE  :  3/4

    TITLE  :  FILES OPEN EXTEND




  MsDos(reg);
  if reg.al<3 then
          begin
          writeln('Extend Unit Require DOS 3.0 or greater');
          halt(1);
          end;

                  {Reset the FreePtr}
                  {This  reduces  the  heap  space  used  by  Turbo
  Pascal}
  if Ofs(FreePtr^)<>0 then
  {Checks to see if the Heap is empty}
          begin
          write('Heap   must   be   empty   before    Extend   unit
  initializes');
          writeln;
          halt(1);
          end;
  FreePtr:=ptr(Seg(FreePtr^)-(Handles div 8 +1), Ofs(FreePtr^));

                  {Determine  how  much  memory  is   allocated  to
  program}
  {Reg.Bx will return how many paragraphs used by program}
  reg.ah:=$4A;
  reg.es:=PrefixSeg;
  reg.bx:=$FFFF;
  msdos(reg);

                  {Set  the  program  size  to  the  allow  for new
  handles}
  reg.ah:=$4A;
  reg.es:=PrefixSeg;
  reg.bx:=reg.bx-(Handles div 8 +1);
  msdos(reg);

                  {Error when a Block Size is not appropriate}
  if (reg.flags and 1)=1 then
          begin
          Writeln('Runtime Error ',reg.ax);
          Writeln('In the Extend Unit');
          halt(1);
          end;














  PRODUCT  :  TURBO PASCAL                           NUMBER  :  545
  VERSION  :  4.0, 5.0, AND 5.5
       OS  :  PC-DOS 3.0 or later, MS-DOS 3.0 or later
     DATE  :  February 28, 1992                        PAGE  :  4/4

    TITLE  :  FILES OPEN EXTEND




                  {Allocate Space for Additional Handles}
  reg.ah:=$67;
  reg.bx:=Handles;
  MsDos(reg);
  end.

  Write the following program  to  a  separate  file.  This program
  tests the  extend  unit.    This  test  should be done on systems
  equipped with a hard disk.

  program TestEx;
  uses extend;
  type
          filearray=array[1..250] of text;
  var
          f:^filearray;
          i:integer;
          s:string;

  begin
                  {Allocate Space for File Variable Table}
  new(f);
                  {Open 250 files simultaneously}
  for i:=1 to 250 do
          begin
          str(i,s);
          Assign(f^[i],'Dum'+s+'.txt');
          rewrite(f^[i]);
          writeln('Open #',s);
          end;

                  {Write some text to the files}
  for i:=1 to 250 do
          write(f^[i],'This is a test file');

                  {Close the files}
  for i:=1 to 250 do
          begin
          close(f^[i]);
          writeln('Closing #',i);
          end;

                  {Erase the files}













  PRODUCT  :  TURBO PASCAL                           NUMBER  :  545
  VERSION  :  4.0, 5.0, AND 5.5
       OS  :  PC-DOS 3.0 or later, MS-DOS 3.0 or later
     DATE  :  February 28, 1992                        PAGE  :  5/4

    TITLE  :  FILES OPEN EXTEND




  for i:=1 to 250 do
          begin
          erase(f^[i]);
          writeln('Erasing #',i);
          end;

  end.