Using INTDOSQQ for Keyboard Input in FORTRAN 5.1

• Microsoft FORTRAN Compiler for MS-DOS, version 5.1

SUMMARY

This article provides information and sample code on how to check for the presence of keyboard input and get the keybord input with (or without) echoing the keys to the screen.

MORE INFORMATION

Page 273 of the Microsoft FORTRAN version 5.1 "Reference" manual explains how to use the INTDOSQQ and INTDOSXQQ subroutines to invoke MS-DOS Interrupt 21h system calls. Two of these Int 21h functions, functions 7 and 8, get input from the keyboard without echoing that input to the display. The difference between these two functions is that function 7 ignores CTRL+C and CTRL+BREAK characters while function 8 handles these characters by breaking out of the program. The function B (hex) checks to see if a key was pressed. It will return true if a key is waiting to be read, and false if it is called after all of the keys have been read.

What the Sample Code Does

The sample code function GETCH uses MS-DOS Int 21h, function 8 to get a character from Standard Input without echoing it to the screen.

The sample code subroutine PUTCHAR uses Int 21h function 2 to write a single character to the screen.

The sample code PASSWORD uses GETCH to allow input of a password without echoing the keystrokes to the display. PUTCHAR is used to display an asterisk for each keystroke entered.

The sample code function KBHIT uses Int 21h function B(hex) to check if a key was pressed. It returns 0 if no key is available and returns non-zero if a key was pressed. Use GETCH to get the key(s).

NOTE: If several of the routines are put into the same file, then the statement:

   include 'flib.fi'

Sample Code: GETCH

C Compile options needed: none

      include 'flib.fi'
      integer*2 function getch
      include 'flib.fd'
      record /regs$info/ in,out
      in.bregs.ah=#08             ! Function 8 - STDIN Input (no echo)
      call intdosqq(in,out)       ! Int 21h
      getch=out.bregs.al          ! Input data returned in AL
      return
      end

Sample Code: PUTCHAR

C Compile options needed: none

      include 'flib.fi'
      subroutine putchar( ch )
      include 'flib.fd'
      record /regs$info/ in,out
      character*1 ch
      in.bregs.ah=#02             ! Function 2 - Display Output
      in.bregs.dl=ch              ! Character to display goes in DL
      call intdosqq(in,out)       ! Int 21h
      return
      end

Sample Code: PASSWORD

C Compile options needed: none

      include 'flib.fi'
      program password
      character*80 pass
      logical get_pass/.true./
      integer*2 i,j,getch

      write(*,'(1x,a,\)') 'ENTER PASSWORD > '
      i=1
      do while (get_pass)
         j=getch()                  ! Get a character of the password
         if (j.le.32) then
            if (j.eq.8.and.i.gt.1) then ! BACKSPACE key pressed
               i=i-1
               call putchar( char(j) )! Move cursor back one character
               call putchar( ' ' )    ! Write a blank over the asterisk
               call putchar ( char(j) )! Move cursor back to blanks
               pass(i:i+1) = '  '
            endif
            if (j.eq.13) get_pass=.false.! ENTER key pressed -- exit
         else
            call putchar( '*' )        ! Echo asterisk to display
            pass(i:i)=char(j)          ! Add input character to string
            i=i+1
            if (i.gt.80) get_pass=.false. ! Don't write past string end
         endif
      enddo
      write(*,*)
      write(*,*) 'password entered > ',pass
      end

Sample Code: KBHIT

C Compile options needed: none

      include 'flib.fi'
      integer*2 function kbhit
      include 'flib.fd'
      record /regs$info/ in,out
      in.bregs.ah=#0B             ! Function B - Get STDIN Status
      call intdosqq(in,out)       ! Int 21h
      kbhit=out.bregs.al          ! Input data returned in AL
      return
      end

REFERENCES

For detailed information about the various Int 21h functions, consult any MS-DOS programmer's reference manual.