Is it possible to use dynamic arrays in gpc?

[Ohonin Yuriy]

Hello.

I'm trying to use such a code:

type
        TVar = object
                param1, param2:string;
                ....
        end;

        TVarList = object
                Items:array of TVar;
                count:cardinal;
                .....
        end;

In Delphi  and FPC it works fine, but in GPC i get an error

45: warning: missing string capacity -- assuming 255
49: error: syntax error before `of'

Is it possible to use dynamic arrays in gpc?
I had searched gpc manual, but it is not clear for me - may be, it is
 possible to use dynamic array only as function parametr? It seems to be a
 little strange - dynamic arrays are a very old feature :(


--
Best regards, Yuriy Ohonin.

[Jonas Maebe-2]

On 05 Feb 2008, at 05:43, Ohonin Yuriy wrote:

> I had searched gpc manual, but it is not clear for me - may be, it is
>  possible to use dynamic array only as function parametr? It seems  
> to be a
>  little strange - dynamic arrays are a very old feature :(

You are confusing open arrays and dynamic arrays. Open arrays are an  
established feature, dynamic arrays are a Delphi invention. See e.g.  
this page for an explanation of the difference:
http://rvelthuis.de/articles/articles-openarr.html


Jonas

[Adriaan van Os-7]

Ohonin Yuriy wrote:

> Hello.
>
> I'm trying to use such a code:
>
> type
> TVar = object
> param1, param2:string;
> ....
> end;
>
> TVarList = object
> Items:array of TVar;
> count:cardinal;
> .....
> end;
>
> In Delphi  and FPC it works fine, but in GPC i get an error
>
> 45: warning: missing string capacity -- assuming 255
> 49: error: syntax error before `of'
>
> Is it possible to use dynamic arrays in gpc?

See section [6.2.11.5 EP’s Schema Types including ‘String’] of the gpc manual.

ISO 10206 Extended Pascal feature.

type
        RealArray (n: Integer) = array [1 .. n] of Real;
        Matrix (n, m: PositiveInteger) = array [1 .. n, 1 .. m] of Integer;

The type ‘RealArray’ in this example is called a Schema with the discriminant ‘n’.
To declare a variable of such a type, write:

var
        Foo: RealArray (42);

Regards,

Adriaan van Os

[Waldek Hebisch]

Ohonin Yuriy wrote:

> I'm trying to use such a code:
>
> type
> TVarList = object
> Items:array of TVar;
> count:cardinal;
> .....
> end;
>
> In Delphi  and FPC it works fine, but in GPC i get an error
>
> 45: warning: missing string capacity -- assuming 255
> 49: error: syntax error before `of'
>
> Is it possible to use dynamic arrays in gpc?

gpc does not implement Delphi style dynamic arrays.  As Adriaan
wrote you can get very similar functionality using Extended
Pascal schema and pointers.  Of course Extended Pascal schema
have quite different syntax.  Also memory management is different:
with pointers to schema you must manually deallocate arrays.

--
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hebisch@...

[Ohonin Yuriy]

On Tuesday 05 February 2008 17:13, you wrote:

> Ohonin Yuriy wrote:
> > Hello.
> >
> > I'm trying to use such a code:
> >
> > type
> > TVar = object
> > param1, param2:string;
> > ....
> > end;
> >
> > TVarList = object
> > Items:array of TVar;
> > count:cardinal;
> > .....
> > end;
> >
> > In Delphi  and FPC it works fine, but in GPC i get an error
> >
> >
> > 49: error: syntax error before `of'
> >
> > Is it possible to use dynamic arrays in gpc?
>
> See section [6.2.11.5 EP’s Schema Types including ‘String’] of the gpc
> manual.
>
> ISO 10206 Extended Pascal feature.
>
> type
> RealArray (n: Integer) = array [1 .. n] of Real;
> Matrix (n, m: PositiveInteger) = array [1 .. n, 1 .. m] of Integer;
>
> The type ‘RealArray’ in this example is called a Schema with the
> discriminant ‘n’. To declare a variable of such a type, write:
>
> var
> Foo: RealArray (42);
>
> Regards,
>
> Adriaan van Os

Thank you, but will i be able to change array length during runtime in this
case?
Hear is my goals:
I need a list of objects.
I need to add a new object to this list at run time. (this could be slow)
I need quik access to any object. So it will be no good to use pointers like

type
   PListElement = ^TListElement;
   TListElement = object
         ...
         next,
         previos:PListElement;
         ...
   end;

Also, what about

45: warning: missing string capacity -- assuming 255

--
Yuriy

[Russell Whitaker]

On Wed, 6 Feb 2008, Ohonin Yuriy wrote:

[...]
>
> Also, what about
>
> 45: warning: missing string capacity -- assuming 255
>
Use a type.
Examples:

   type
     string80 = string( 80 );
     alongstring = string( 100000 );

Russ

[Ohonin Yuriy]

On Thursday 07 February 2008 00:47, Russell Whitaker wrote:

> On Wed, 6 Feb 2008, Ohonin Yuriy wrote:
>
> [...]
>
> > Also, what about
> >
> > 45: warning: missing string capacity -- assuming 255
>
> Use a type.
> Examples:
>
>    type
>      string80 = string( 80 );
>      alongstring = string( 100000 );
>
> Russ

The main advandage of Pascal is that strong typization mekes working whith
pointers and dynamic structures very easy. If i need to write my own class
for Normal Strings, and for most of functions to work whith it - it is better
switch to fpc, or just c++ - it's already written.

Farewell.

--
Yuriy

[Waldek Hebisch]

Ohonin Yuriy wrote:
>
> The main advandage of Pascal is that strong typization mekes working whith
> pointers and dynamic structures very easy. If i need to write my own class
> for Normal Strings, and for most of functions to work whith it - it is better
> switch to fpc, or just c++ - it's already written.
>

Well, currently gpc support trurly dynamic strings (and arrays) only
via pointers, like:

type
    StrPtrT = ^String;

function blanks(n : integer) : StrPtrT;
var result : StrPtrT;
    i : integer;
begin
    new(result, n);
    for i := 1 to n do
       result[i] := ' ';
    blanks := result;
end;

You may look at the 'stringschemademo.pas' demo program to see
some possibilites offered by gpc strings.

--
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hebisch@...