Gpc March 2003

gpc@gnu.de

23 participants
45 discussions

Range Checking
by Frank Heckenbach 05 Mar '03

05 Mar '03

Hi, after some friendly requests and discussion, I'm planning to implement range checking as one of the next major things in GPC (probably in Januaray, if nothing urgent gets in between ...). Note, I'm using "range checking" in the specific meaning I explained recently, not generally for all kinds of runtime checks, and not including overflow checking of arithmetic operations etc. (that will be a separate issue). Also, as I said before, I'll do an "easy" implementation. I'm still not convinced that anything more is worth the (big) effort when the programmer in the rare (AFAICS) cases where it matters could just as well use explicit types etc. to avoid checks where he doesn't want them. Since some of you have said they'd like to help, but can't code in the compiler itself, here are at least 2 chances: 1. Help finding all places where range checking must be applied In mean this from a Pascal point of view, covering, of course, all standards, dialects and extensions that GPC supports. So far I've found the following ones: - assignment to variables and function results, - value parameter passing to user-defined and built-in (e.g., `Chr', `FillChar', ...) routines, - array indexing (R/W), - array slice indexing (R/W), - `for' loop bounds, - conformant array range, - actual schema discriminants, - initialization of types, variables and typed constants, - `asm' targets 2. Write test programs Test programs should follow the guidelines in the manual. In particular, since most of the tests will check for errors, each one must be a separate test for each situation (each of the cases above plus any that others of you will come up with). For a way to test runtime errors see, e.g., fjf424d.pas. Range checking will be on by default, and can be switched on/off with the options `--[no-]range-checking' and the compiler directives `{$[no-]range-checking}', and `{$R+}', `{$R-}'. A complete set of tests should also test all of those. If you'd like to do so, please post a short note, so several of you won't duplicate efforts, but can coordinate. Frank -- Frank Heckenbach, frank(a)g-n-u.de, http://fjf.gnu.de/, 7977168E GPC To-Do list, latest features, fixed bugs: http://www.gnu-pascal.de/todo.html GPC download signing key: 51FF C1F0 1A77 C6C2 4482 4DDC 117A 9773 7F88 1707

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Prefix directives -> attributes
by Frank Heckenbach 04 Mar '03

04 Mar '03

Some directives in GPC are written in prefix form, in particular `static', `volatile', `register' for variables and `inline' for routines, e.g.: inline procedure Foo; var a: static Integer; Since this syntax is also more like C than Pascal, I'd like to turn them into attributes, thereby also making them non-keywords. E.g.: procedure Foo; attribute (inline); var a: Integer; attribute (static); I suppose `static' variables are `inline' routines are used to some extent (but hopefully not too much), the others should be negligible, so the amount of changes necessary should be limited. And since I'm doing the incompatible changes WRT `c', `c_language' and `asmname' now, it might be a good time to do them all at once. Any objections? Frank -- Frank Heckenbach, frank(a)g-n-u.de, http://fjf.gnu.de/, 7977168E GPC To-Do list, latest features, fixed bugs: http://www.gnu-pascal.de/todo.html GPC download signing key: 51FF C1F0 1A77 C6C2 4482 4DDC 117A 9773 7F88 1707

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high comprehension
by Francois Schoubben 03 Mar '03

03 Mar '03

Continuing my tests on range check, i'm rtfm... On the HIGH keyword part, it's said that "For array types or variables of that type, @samp{High} returns the highest index a variable of that type can assume." Same for LOW. So, i'm expecting, in the example --- program highlow; var a : array[1..100]of integer; procedure hilo(ar : array of integer); begin writeln(LOW(ar),' ',HIGH(ar)) end; begin hilo(a); end. --- that it write 1 100 but it's currently saying 0 99 Why not, but, i think it's not what's said in the documentation... Am i still "out of the game"? Am i using a too old version?

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Standard question: `New' with variant records
by Frank Heckenbach 03 Mar '03

03 Mar '03

Another standard question. Is the following valid: program Foo; type t = record case Integer of 1: () end; var v: ^t; begin New (v, 2) end. Some of GPC's test programs (not written by me) do something like this, but I doubt whether that's ok. As usual, the language of the standard (6.7.5.3 in EP) is somewhat confusing, so I'm better asking to be sure ... Another thing: The standard allows to set variant tags or schema discriminants in `New', but not both together. Is this an artificial restriction, or would there be some deeper problem with code like this: program Foo; type t (n: Integer) = record case Integer of 1: () end; var v: ^t; begin New (v, 42 { discriminant }, 1 { variant tag }) end. Frank -- Frank Heckenbach, frank(a)g-n-u.de, http://fjf.gnu.de/, 7977168E GPC To-Do list, latest features, fixed bugs: http://www.gnu-pascal.de/todo.html GPC download signing key: 51FF C1F0 1A77 C6C2 4482 4DDC 117A 9773 7F88 1707

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DLL Calling conventions and refering to external functions...
by Dominique Louis 02 Mar '03

02 Mar '03

Hi Eike and any one else who can guide me, When using a DLL or Shared object under Delphi or Kylix the headers tend to have function declarations as... function SDL_Init(flags: UInt32): Integer; cdecl; external 'SDL.dll'; where cdecl is the calling convention and the external key word allows you to specify in which DLL or SO, the function is to be found. Obviously in this case it is 'SDL.dll'. I noticed in Eike's port that he renamed the SDL functions to make them more Pascalised. Is there another way of achieving dynamic linking without going down the rename route? How does GNU Pascal dynamically link to DLLs and how are the Pascal headers defined? Thanks, Dominique. http://www.DelphiGamer.com := go on, write a game instead;

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Gpc March 2003