Gpc April 1997

gpc@gnu.de

24 participants
111 discussions

Re: What is standard, and what isn't?
by Berend de Boer 30 Apr '97

30 Apr '97

Peter Gerwinski wrote: >1) Is the comparision with `=' or `<>' of structured variables okay in > ISO Pascal? ISO 10206 6.8.3.5 only says that the types to be compared > must be compatible. No, see the table in 6.8.3.5. And I see quite some problems in implementing this correctly. A simple byte compare won't do except in the most easiest of cases. If you want something 'difficult' to do , implement integer and string value arrays :-) >2) In GPC strings, the schema discriminant "Capacity" is accessible > as a "record field" of the string. Is this okay by ISO 10206, > and should it be done for other schemata this way, too? Certainly: see the examples in 6.8.4 And how >to > tread the "length" field of a string? ISO 10206 6.4.3.3 does not > say anything about that. I could imagine the string schema type >to > be something similar to > > Type > String ( Capacity: Integer ) = record > length: Integer; > String: packed array [ 1..Capacity ] of Char; > end (* String *); > > except that the "String" field is automatically dereferenced. I think one implements it as: Type String ( Capacity: Integer ) = record length: Integer; String: packed array [ 1..Capacity+SizeOf(Char) ] of Char; end (* String *); +1 to allow for a trailing zero (or zero's in case of Unicode...). However length is not specified in the standard, so it should not be accessible with Extended Pascal. You can always use length(MyStr) to achieve the same functionality. Groetjes, Berend.

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Re: Short strings (Was: Modifying string length?)
by Berend de Boer 30 Apr '97

30 Apr '97

You wrote: >Should it be `ShortString' or `ShortStr'? In analogy to `LongInt' Borland uses ShortString in Delphi so I go for ShortString. Groetjes, Berend.

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Re: Modifying string length?
by Frank Heckenbach 30 Apr '97

30 Apr '97

> I would say: GPC *does* optimize this. Just type `gpc -O -S foo.pas' > and look at `foo.s' ... Hmmm... well, I could not see the effect. I wrote the following test program: program x; var s:string[10000]; begin s:=''; s:=s+'a' end. I compiled it with "-O3 -S". The resulting code contained two calls to _memcpy. Another test program that appended characters in a loop obviously ran in O(n^2). Am I missing something? -- 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

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Re: exit; ????
by Peter Gerwinski 29 Apr '97

29 Apr '97

According to skye: > > Is Exit not included in GPC? i.e. > [...] > I tried using return; and that works. GPC 2.0 only has `return'; newer alpha versions also have `exit'. > I posted this question to the comp.lang.pascal NG and had someone from > Borland tell me that Exit should do the trick (I didn't say I wasn't using > TP tho). :-) > Is exit a Borland thing? It's an UCSD extension. Borland Pascal is based a lot on UCSD Pascal (Units, Strings, Exit, ...). 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]

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Re: Modifying string length?
by Peter Gerwinski 29 Apr '97

29 Apr '97

According to Frank Heckenbach: > > > > No. They are exceptions in yet another way because they have the > > implicit read-only "length" field. > > That's what I meant. If length was made accessible in a normal way, it > would not be an exception. Being an array schema, the presence of the implicit "length" field would make the string an exception. Being a record schema, the implicit dereference of the "string" field when indexing the string makes it an exception. No way out. (However see my other mail.) 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]

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Short strings (Was: Modifying string length?)
by Peter Gerwinski 29 Apr '97

29 Apr '97

According to The African Chief: > According to Frank Heckenbach: > >255 chars max length are sometimes not enough. > But you can use normal GPC strings for that. Just my point: For applications where you need looooong strings, GPC's <=2GB strings with 8 bytes of overhead are perfect. In those cases where you must save space, 255 characters are fine - and they are compatible to UCSD and Borland Pascal. Should it be `ShortString' or `ShortStr'? In analogy to `LongInt' instead of `LongInteger' I would vote for `ShortStr'; OTOH, Prospero's Extended Pascal compiler (PEP) has `ShortString' for this ... 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]

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Re: Modifying string length?
by The African Chief 29 Apr '97

29 Apr '97

On Tue, 29 Apr 1997 12:53:53 +0200 Frank Heckenbach <heckenb(a)mi.uni-erlangen.de> wrote: [...] >> It would not be too difficult to make "MyStr.length" and "MyStr.String" >> accessible "record fields" of strings. Would it be desireable? > >Yes! (At least length; the String part is accessible anyway with s[n].) > >> I am >> not sure how this fits into the standard ... > >I'm not, either. If it conflicts, it should be disabled with >"--extended-pascal", I suppose. It should be disabled, with "-borlland-pascal" as well. >> Another thing *is* planned: A new data type `ShortString' (or >> `ShortStr'?) which will be the UCSD/Borland version of Strings. In many >> contexts, they are better than Extended Pascal string schemata because >> they have only 1 byte overhead instead of 8. (But this will be a lot >> of work. Anybody interested to help here???) > >What about another type with a 2 byte length field (2 instead of 8 bytes >overhead)? Will this be BP compatible? >255 chars max length are sometimes not enough. But you can use normal GPC strings for that. >BTW: I heard >Delphi has some kind of long strings. Anyone knows what they are? Only available with 32-bit versions of Delphi. Sort of dynamically allocated strings. Delphi does all the background work itself (allocating, freeing, sizing, resizing, etc). I think they can be up to 2GB in size. Need to be used with care, because all sorts of things can go wrong if you treat them like normal strings. "Almost" compatible with pChars. You can do something like "PChar (MyLongString)" to pass a long string as a parameter to a function that requires a pChar parameter. When used as parameters or function results in a DLL, all programs that use that DLL must use Delphi's memory manager DLL as well. Personally, I wouldn't touch them with a barge pole. I would rather use a pChar, if that is what I want, or a normal string, if that is what I want - and I prefer to allocate and free memory for data structures myself. Best regards, The Chief Dr Abimbola A. Olowofoyeku (The African Chief, and the Great Elephant) Author of: Chief's Installer Pro v3.12 for Win16 and Win32. Homepage: http://ourworld.compuserve.com/homepages/African_Chief/ E-mail: laa12(a)cc.keele.ac.uk

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Re: Modifying string length?
by Frank Heckenbach 29 Apr '97

29 Apr '97

> I would say: GPC *does* optimize this. Just type `gpc -O -S foo.pas' > and look at `foo.s' ... Fine! I'll take a look at it. > It would not be too difficult to make "MyStr.length" and "MyStr.String" > accessible "record fields" of strings. Would it be desireable? Yes! (At least length; the String part is accessible anyway with s[n].) > I am > not sure how this fits into the standard ... I'm not, either. If it conflicts, it should be disabled with "--extended-pascal", I suppose. > Another thing *is* planned: A new data type `ShortString' (or > `ShortStr'?) which will be the UCSD/Borland version of Strings. In many > contexts, they are better than Extended Pascal string schemata because > they have only 1 byte overhead instead of 8. (But this will be a lot > of work. Anybody interested to help here???) What about another type with a 2 byte length field (2 instead of 8 bytes overhead)? 255 chars max length are sometimes not enough. BTW: I heard Delphi has some kind of long strings. Anyone knows what they are? > > (Are you planning > > to make strings regular schema types then -- regular except for the extended > > syntax that allows s[n]?) > > No. They are exceptions in yet another way because they have the > implicit read-only "length" field. That's what I meant. If length was made accessible in a normal way, it would not be an exception. -- Frank Heckenbach, Erlangen, Germany heckenb[No_Spam! Remove this to reply.](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

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Re: Modifying string length?
by Peter Gerwinski 28 Apr '97

28 Apr '97

According to Frank Heckenbach: > > Well, the problem is, I said "efficiently". > I don't assume, gpc would optimize statements like > s:=s+'a' > where s is a (possibly quite long) string, so I'd have O(n) where actually > O(1) is possible. I would say: GPC *does* optimize this. Just type `gpc -O -S foo.pas' and look at `foo.s' ... > E.g. the examples from the documentation about converting > CStrings to Pascal strings append char by char in a loop -- O(n^2) instead > of O(n). I don't think that should be left as it is. You mean the routines in the FAQ? I think they are O(n) because "S:= S + Src^" is inlined and optimized. But of course, feel free to improve those routines and send the result to Jan-Jaap ... ;-) > I'd have to do it like this if there's no other way... > But shouldn't it be possible to access the fields of the "string record" in > a direct way? Perhaps in the course of the schema project? It would not be too difficult to make "MyStr.length" and "MyStr.String" accessible "record fields" of strings. Would it be desireable? I am not sure how this fits into the standard ... Another thing *is* planned: A new data type `ShortString' (or `ShortStr'?) which will be the UCSD/Borland version of Strings. In many contexts, they are better than Extended Pascal string schemata because they have only 1 byte overhead instead of 8. (But this will be a lot of work. Anybody interested to help here???) > (Are you planning > to make strings regular schema types then -- regular except for the extended > syntax that allows s[n]?) No. They are exceptions in yet another way because they have the implicit read-only "length" field. 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]

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Peter Gerwinski wrote:
by Frank Heckenbach 28 Apr '97

28 Apr '97

> > Is there a way to change a string's length directly? > > AFAIK, there isn't. Use the `SubStr' function (like BP's `copy' function) > to shorten a string, and the `+' operator to make it longer. Well, the problem is, I said "efficiently". I don't assume, gpc would optimize statements like s:=s+'a' where s is a (possibly quite long) string, so I'd have O(n) where actually O(1) is possible. E.g. the examples from the documentation about converting CStrings to Pascal strings append char by char in a loop -- O(n^2) instead of O(n). I don't think that should be left as it is. > And of course you can take a pointer to the string, cast it to a pointer > to a record the fields of which you can manipulate like you wish ... I'd have to do it like this if there's no other way... But shouldn't it be possible to access the fields of the "string record" in a direct way? Perhaps in the course of the schema project? (Are you planning to make strings regular schema types then -- regular except for the extended syntax that allows s[n]?) -- Frank Heckenbach, Erlangen, Germany heckenb[No_Spam! Remove this to reply.](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

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Gpc April 1997