May 1997 - Gpc

Short Strings, Schema discriminants, UCSD Pascal (Was: Modifying string length?)
by Frank Heckenbach 08 May '97

08 May '97

Peter Gerwinski wrote: > > BP 7.0 allows this via High(s) -- is something like BP's High and Low > > functions (to give the lower and upper bounds of arrays and subrange types) > > present or planned for gpc? [...] > > Yes. Planned, this is? Doesn't seem to be present (or different names?). -- Frank Heckenbach, Erlangen, Germany heckenb(a)mi.uni-erlangen.de Turbo Pascal: http://www.mi.uni-erlangen.de/~heckenb/programs.htm Internet links: http://www.mi.uni-erlangen.de/~heckenb/links.htm

1 0

Cancel from the List
by Walter Schaufelberger 06 May '97

06 May '97

Please delete me from the gpc member list. The user for this compuserve adress has changed and im not interested in gpc W. Schufelberger

1 0

Short Strings, Schema discriminants, UCSD Pascal (Was: Modifying string length?)
by Peter Gerwinski 05 May '97

05 May '97

According to Frank Heckenbach: > > [...] Then perhaps it would be > useful to allow the same syntax also for ShortStrings (additionally), just > as if ShortString[n] was declared as: > > record > case boolean of > false:(CurrentLength:byte); > true:(string:array[0..n] of char); > end; > > Also, it could be good to provide a (read-only) "pseudo field" Capacity. > [...] > These two things would make ShortStrings more similar to (and often > exchangeable with) LongStrings, without giving up BP compatibility. Good ideas, but a lot of work ... > (BTW: LongStrings' Capacity is always read-only, isn't it?) It is not. Probably it should be - somebody knows? And for other schema discriminants? > BP 7.0 allows this via High(s) -- is something like BP's High and Low > functions (to give the lower and upper bounds of arrays and subrange types) > present or planned for gpc? [...] Yes. > [...] So, perhaps better forget about the #0 with ShortStrings, and add > it when converting to other strings... I think that's the way to go. > But UCSD was non-standard, too, wasn't it? Just out of curiosity, it doesn't > really matter to me. UCSD Pascal was developed at the University of California San Diego (UCSD), not by a company, that's why I consider it as a well-defined standard, although no ISO standard. I have read about a company "SofTech" distributing UCSD Pascal, and I got mine from Apple as "Apple Pascal". If somebody has some more exact information, I would be glad to know. Greetings, Peter Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer peter.gerwinski(a)uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201] maintainer GNU Pascal [970420] - http://home.pages.de/~gnu-pascal/ [970125]

2 1

Re: Portability questions (Arrays)
by Berend de Boer 04 May '97

04 May '97

Frank Heckenbach wrote: >Two questions about portability of properties of arrays: >1. Is it safe to assume -- for all platforms, including possible future > ones -- that SizeOf(a) = ((Ord(y)-Ord(x)+1) * SizeOf(t)? No. > 2. Is it safe to assume that > Integer(@a[p])-Integer(@a[q]) = (p-q) * SizeOf(t)? No. > (Is it generally allowed to cast a pointer into an integer, > in the first place?) No. Groetjes, Berend.

1 0

Re: ClrScr
by Peter Gerwinski 03 May '97

03 May '97

According to Herbert Voss: > > how can I clear the screen under gpc? Just like > Borlands ClrScr. On the DOS/DJGPP platform, use `ClrScr' from the `CRT' Unit of the "BPcompat" package, available at ftp://kampi.hut.fi/jtv/gnu-pascal/contrib/bpcompat.zip ftp://agnes.dida.physik.uni-essen.de/gnu-pascal/contrib/bpcompat.zip You can also try the portable `BO5' library, available at ftp://kampi.hut.fi/jtv/gnu-pascal/contrib/bo5/ ftp://agnes.dida.physik.uni-essen.de/gnu-pascal/contrib/bo5/ `BO5' has a `Displays' Unit which implements a `ClearScreen' procedure which does essentially the same as `ClrScr'. We are still looking for somebody who wants to implement a portable, Borland-compatible `CRT'. (But our `Graph' Unit, "BGI2GRX", works on Linux at least.:) Hope this helps, Peter Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer peter.gerwinski(a)uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201] maintainer GNU Pascal [970420] - http://home.pages.de/~gnu-pascal/ [970125]

1 0

BP-style ^X character constants
by Peter Gerwinski 03 May '97

03 May '97

Hello, I proudly announce that the next alpha version of GPC will understand BP-style character constants: ^A means chr ( 1 ) i.e. Ctrl+A, etc. Thanks to GPC's context-sensitive lexical analyzer, they work even better than in BP. GPC just compiled Type X = ^Y; (* Forward pointer reference *) Y = array [ ^A..^Z ] of ^Z; (* An array of pointers to Z *) Z = ^A..^Z; (* Subrange chr(1)..chr(26) *) Now try to compile this with Borland Pascal 7.0 ... ;-) Hooray, Peter Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer peter.gerwinski(a)uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201] maintainer GNU Pascal [970420] - http://home.pages.de/~gnu-pascal/ [970125]

1 0

TFDDs - customizing `writeln' (Was: Legal Change in GPC ?)
by Peter Gerwinski 03 May '97

03 May '97

According to Frank Heckenbach: > > Indeed, I'd like to have something like this in gpc, too. I'm not at all > familiar with the internals of "Text" files (or other files) in gpc. > (ISTR, it has something to do with "bindable" variables, but I don't know > much about those, either.) > > [...] > > The particular syntax (and other things) BP uses for this is, IMHO, not very > nice (it was introduced after the "good days" of Borland, but before the > introduction of OOP, which could have simplified things), so I don't vote > for copying BP's mechanism. But any way to do such things would be good. If somebody who knows C wants to implement this for GPC, here are some ideas: GPC's run time system (RTS) defines a function `_p_write' which is responsible for all output to text files. The C source is in `rts/rts-write.c'. I already modified this function to call `cprintf' instead of `printf' on the DOS platform if the variable `_p_directvideo' has a nonzero value. This is done through some preprocessor macros PRINTF1, ... PRINTF4, CFWRITE and serves the purpose to make a `CRT' Unit for DOS possible. If you replace my macro calls by a call to `sprintf' followed by an indirect call to an output function, we've got it. (Note that Pascal allows `chr ( 0 )' characters in Strings.) Happy hacking, Peter Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer peter.gerwinski(a)uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201] maintainer GNU Pascal [970420] - http://home.pages.de/~gnu-pascal/ [970125]

1 0

Re: Portability questions (Arrays)
by Peter Gerwinski 03 May '97

03 May '97

According to Frank Heckenbach: > > 1. Is it safe to assume -- for all platforms, including possible future > ones -- that SizeOf(a) = ((Ord(y)-Ord(x)+1) * SizeOf(t)? I first thought that this would not be the case due to alignment problems, but ...: That's *exactly* the way how GPC calculates the size of an array. Why is this so, e.g. with an array of something which has 3 bytes? Program Test; Type r = packed record x: ShortWord; y: Byte; end (* r *); Var x: packed array [ 1..1000 ] of r; begin writeln ( SizeOf ( x ) ); writeln ( SizeOf ( x [ 1 ] ) ); end. The output is 4000 and ... 4. To avoid alignment problems in an "array of r", the record `r' has size 4, not 3. I conclude that the assumption is safe. > 2. Is it safe to assume that > Integer(@a[p])-Integer(@a[q]) = (p-q) * SizeOf(t)? Yes, for the same reason. If the "natural" size of `t' would cause alignment problems, `t' is blown up by GPC. > (Is it generally allowed to cast a pointer into an integer, > in the first place?) I think so. The GNU coding standard says about GCC's (and thus GPC's) behaviour: You can assume that all pointers have the same format, regardless of the type they point to, and that this is really an integer. Greetings, Peter Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer peter.gerwinski(a)uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201] maintainer GNU Pascal [970420] - http://home.pages.de/~gnu-pascal/ [970125]

1 0

page procedure bug?
by Kevin A. Foss 03 May '97

03 May '97

Hello, The discussion of 'clrscr' caused me to look into GPC's support of the page procedure. [On all of the Pascal variants I've used in the past -- I've never used any Borland variant -- 'page' would effectively clear the screen.] While GPC on the other hand seems to follow the standard literally and output just a FF (ASCII 12). No problem there, but the problem is that GPC gives a parse error if use just 'page' but accepts 'page(output)'. My reading of the standard is that page with no parameters should assume standard output, at least if output is explicitly declared in the program heading. (ISO 7185 6.9.5) E.g. this program should compile: program pagetest(output); begin page; end. -Kevin -- Kevin A. Foss --- kfoss(a)mint.net --

1 0

ClrScr
by Herbert Voss 03 May '97

03 May '97

Hello, how can I clear the screen under gpc? Just like Borlands ClrScr. Thanks Herbert

1 0