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From: trevor@ccc.govt.nz
Newsgroups: comp.lang.fortran
Subject: Re: character function subprogram
Message-ID: <1991Apr15.140403.210@ccc.govt.nz>
Date: 15 Apr 91 20:11:57 GMT
References: <1991Apr7.200854.25446@math.ufl.edu>
Lines: 44

In article <1991Apr7.200854.25446@math.ufl.edu>, wang@math.ufl.edu writes:
> Can anyboby explain to me why the following FORTRAN character function
> subprogram works under VAX/VMS, but doesn't work under unix (SunOS 4.1.1,
> Sun Fortran 1.3)? 
> 
>       CHARACTER*8 cursor,cls*4
>       cls = CHAR(27)//'[2J'
>       i   = 5
>       j   = 35
>       PRINT *,cls,cursor(i,j),'I am here!'
>       END
> 
>       CHARACTER FUNCTION cursor*8(row,col)
>       CHARACTER*1 esc,c1*2,c2*2
>       INTEGER row,col
>       esc = CHAR(27)
>       WRITE(c1,'(i2.2)') row
>       WRITE(c2,'(i2.2)') col
>       cursor = esc//'['//c1//';'//c2//'H'
>       RETURN
>       END
> 
> (Unix messages deleted...)
> 

I think the main problem is that direct screen addressing; direct cursor
positioning are system-dependent: even worse, they are peripheral-dependent.
The program quoted writes an output string which contains an ANSI
device-control escape sequence. It should work fine if sent to a DEC VT100,
VT200, VT300 terminal (or any other VDU which emulates a DEC ANSI CRT or 
accepts ANSI device control) by a system which passes on the escape sequence
uncorrupted, but it won't work right on a VT52 or a printer, I think the screen
control sequences for HP terminals were different (but it's a looong time since
I programmed for one) and I'd be surprised if it did work under Unix on a Sun.
Direct cursor addressing isn't standard Fortran. (Fortran carriage-controls for
printers IS standard, but we have one printer that doesn't recognise them...)

I do know you can't use any sort of direct cursor addressing when writing for 
GEM; you have to use the appropriate GEM VDI or AES call.

I know this doesn't HELP much, but I hope it might explain a little.

Trevor Ingham, Systems Programmer, Christchurch City Council, New Zealand.
trevor@ccc.govt.nz