Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-17 Thread Reinier Olislagers 
On 16/03/2014 20:29, Fred van Stappen wrote:
 Many bedankt Harry . ;-)

De rien Jean-Jacques-Loup-Cristophe!

(not getting the name thing but wanting to enter into the spirit of the
things)

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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-17 Thread Fred van Stappen 
 (not getting the name thing but wanting to enter into the spirit of the
 things)

PS :  Cfr your studies in Poudlard school... :-)
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-16 Thread Reinier Olislagers 
On 15/03/2014 12:21, Fred van Stappen wrote:
 I thought that it was mentioned there somewhere already...
 If nit feel free to add it. That's what a wiki is good for afterall. ^^
 
 Done.
 
 = http://wiki.freepascal.org/shared_library

I think I've spotted a mistake in the wiki.

I've adjusted the description of InLibFreeString according to Sven's
previous post:
And, for freeing the allocated memory, you may add this procedure in
the main application : 
=
And, for freeing the allocated memory, you may add this procedure in
the library, which you can then call from your main application : 
and adjusted the rest of the text accordingly...

Of course, please feel free to adjust.
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-16 Thread Fred van Stappen 
 Date: Sun, 16 Mar 2014 10:43:17 +0100
 From: reinierolislag...@gmail.com
 To: fpc-pascal@lists.freepascal.org
 Subject: Re: [fpc-pascal] Library.StringFunction() : PChar = NO
 
 On 15/03/2014 12:21, Fred van Stappen wrote:
  I thought that it was mentioned there somewhere already...
  If nit feel free to add it. That's what a wiki is good for afterall. ^^
  
  Done.
  
  = http://wiki.freepascal.org/shared_library
 
 I think I've spotted a mistake in the wiki.
 
 I've adjusted the description of InLibFreeString according to Sven's
 previous post:
 And, for freeing the allocated memory, you may add this procedure in
 the main application : 
 =
 And, for freeing the allocated memory, you may add this procedure in
 the library, which you can then call from your main application : 
 and adjusted the rest of the text accordingly...
 
 Of course, please feel free to adjust.

Many bedankt Harry . ;-)
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-15 Thread Sven Barth 
Am 14.03.2014 23:46 schrieb Fred van Stappen fi...@hotmail.com:

  Date: Fri, 14 Mar 2014 23:11:14 +0100
  From: pascaldra...@googlemail.com

  To: fpc-pascal@lists.freepascal.org
  Subject: Re: [fpc-pascal] Library.StringFunction() : PChar = NO
 
  On 14.03.2014 22:07, Fred van Stappen wrote:
It's not a problem, as long as you provide an API to dispose the
memory
used by the returned PChar.
The responsibility of calling this API is delegated
to the application.
  
   Yep, with pleasure,... but how to provide an API (and what do you mean
   with provide an API to dispose the memory) ?
  
   = In short, what must i code to do that ?
 
  Inside your library you normally do this when creating a string result:
 
  === code begin ===
 
  function InLibStringFunction: PChar; // of course declared as cdecl ;)
  const
  MyString: AnsiString = 'Hello World'; // this string could also come
  frome somewhere else in your library
  begin
  Result := GetMem(Length(MyString) + 1);
  Move(@MyString[1], Result, Length(MyString));
  Result[Length(MyString)] := 0;
  end;
 
  === code end ===
 
  Note: if your MyString is valid through the complete lifetime it could
  be used you can also use Result := PChar(MyString); instead, but if
  your string is e.g. a variable inside the function or a variable inside
  another function you must copy its content.
 
  If you now allocated a PChar using GetMem you add this function as well
  and export it from the library:
 
  === code begin ===
 
  procedure InLibFreeString(aStr: PChar);
  begin
  FreeMem(aStr);
  end;
 
  === code end ===
 
  One could of course now extend the API with additional checks. E.g. so
  that you know that the string was really allocated by the library and
  not by e.g. the program using it. But maybe the heap manager already
  checks this, I don't know currently.
 
  Regards,
  Sven

 Yep, Sven, excellent and hyper clear.

 Hum, i think that this code must go somewhere in wiki.
 If you agree i will add it into fpc wiki.

I thought that it was mentioned there somewhere already... If nit feel free
to add it. That's what a wiki is good for afterall. ^^

Regards,
Sven
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-15 Thread Sven Barth 
Am 15.03.2014 00:08 schrieb Fred van Stappen fi...@hotmail.com:

  Note: if your MyString is valid through the complete lifetime it could
  be used you can also use Result := PChar(MyString);

 Hum, to be sure that i understand...

 type
   TStringClass = class(TObject)
 Name: AnsiString;   does not change
 SomeText: AnsiString; / may change..
   end;

 var
 AStringClass : TStringClass;

 

 function GetName: PChar;  cdecl ;
 begin
 result := PChar(AStringClass.Name);
 end;

 function GetSomeText: PChar;  cdecl ;
 var
MyString: AnsiString ;
 begin
  MyString := AStringClass.SomeText ;

Result := GetMem(Length(MyString) + 1);
Move(@MyString[1], Result, Length(MyString));
Result[Length(MyString)] := 0;
 end;

 Is it OK ?

You don't need the MyString variable, you can simply use
AStringClass.SomeText. The variable was just for illustrations.

And you should definitely document the results of which of your libraries
must be freed and which must not.

Additionally I would suggest to store the pointer values of the allocated
PChar results (e.g. TList or specialize TFPGListPChar) so that you can
use this inside your exported FreeString function to check whether this is
indeed a pointer that you need to free.

Regards,
Sven
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-15 Thread Fred van Stappen 
I thought that it was mentioned there somewhere already... 
 If nit feel 
free to add it. That's what a wiki is good for afterall. ^^

Hum, never seen... I will add it ASAP ;-)

 You don't need the MyString variable, you can simply use 
 AStringClass.SomeText.

= OK

 And you should definitely document the results of which
 of your libraries must be freed and which must not.

 Additionally I would suggest to store the pointer values of the allocated
PChar results


= Yep, good idea, i will do it.


One more time, tetra thanks Sven.


Fred

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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-15 Thread Fred van Stappen 
 I thought that it was mentioned there somewhere already...
 If nit feel free to add it. That's what a wiki is good for afterall. ^^

Done.

= http://wiki.freepascal.org/shared_library

Many thanks Sven.
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-14 Thread leledumbo 
 It will be the memory manager of the library who deals with the PChar
result.
So difficult for the main application to manage the memory used by PChar.

It's not a problem, as long as you provide an API to dispose the memory used
by the returned PChar. The responsibility of calling this API is delegated
to the application.

 MyStrTest(inStr:Pchar; outStr:pChar; size:integer):integer; cdecl;  
 var 
   MyRealResult :string;
 begin
  MyRealResult :=   inStr + ' added by function ';
   Result := length(myRealResult);
 if size = result then move(OutStr[0], MyRealResult[1], result);
 end;

Wrong usage of Move
(http://www.freepascal.org/docs-html/rtl/system/move.html). First parameter
is source, second is destination. So you have to swap them in above
function.

 function  testLib(InputText : string) : string ;
 var
  MyStrOut : string;
   MyLen : integer;
 begin
MyLen := MyStrTest( @InputText[1],@MyStrOut[1], 0);
SetLEngth(MyStrOut, mylen+1); 
FillChar(MyStrOut[1], MyLen+1,0);
MyStrTest(@InputText[1], @MyStrOut[1], 0);
  result := MyStrOut ;
 end;

Wrong usage of the MyStrTest. Here you give Size parameter of value 0, while
in MyStrTest... see that last if statement? Guess yourself. Moreover, after
the first call, you set the length and then filling the space with 0. The
2nd MyStrTest call doesn't differ from the first.

From the code, I can guess what that good guru means. First call he just
wants to get the length, therefore giving size 0. He then allocates enough
storage and re-call the function, but this time he seems to have a typo. The
2nd MyStrTest call should have size parameter set to MyLen.



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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-14 Thread Fred van Stappen 
 Date: Fri, 14 Mar 2014 08:20:46 -0700
 From: leledumbo_c...@yahoo.co.id
 To: fpc-pascal@lists.freepascal.org
 Subject: Re: [fpc-pascal] Library.StringFunction() : PChar = NO
 
  It will be the memory manager of the library who deals with the PChar
 result.
 So difficult for the main application to manage the memory used by PChar.
 
 It's not a problem, as long as you provide an API to dispose the memory used
 by the returned PChar. The responsibility of calling this API is delegated
 to the application.
 
  MyStrTest(inStr:Pchar; outStr:pChar; size:integer):integer; cdecl;  
  var 
MyRealResult :string;
  begin
   MyRealResult :=   inStr + ' added by function ';
Result := length(myRealResult);
  if size = result then move(OutStr[0], MyRealResult[1], result);
  end;
 
 Wrong usage of Move
 (http://www.freepascal.org/docs-html/rtl/system/move.html). First parameter
 is source, second is destination. So you have to swap them in above
 function.
 
  function  testLib(InputText : string) : string ;
  var
   MyStrOut : string;
MyLen : integer;
  begin
 MyLen := MyStrTest( @InputText[1],@MyStrOut[1], 0);
 SetLEngth(MyStrOut, mylen+1); 
 FillChar(MyStrOut[1], MyLen+1,0);
 MyStrTest(@InputText[1], @MyStrOut[1], 0);
   result := MyStrOut ;
  end;
 
 Wrong usage of the MyStrTest. Here you give Size parameter of value 0, while
 in MyStrTest... see that last if statement? Guess yourself. Moreover, after
 the first call, you set the length and then filling the space with 0. The
 2nd MyStrTest call doesn't differ from the first.
 
 From the code, I can guess what that good guru means. First call he just
 wants to get the length, therefore giving size 0. He then allocates enough
 storage and re-call the function, but this time he seems to have a typo. The
 2nd MyStrTest call should have size parameter set to MyLen.

@ leledumbo, like always = brilliant = Tetras * Megas thanks. ;-)
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-14 Thread Fred van Stappen 
 It's not a problem, as long as you provide an API to dispose the memory
 used by the returned PChar.
 The responsibility of calling this API is delegated
 to the application.

Yep, with pleasure,... but how to provide an API (and what do you mean with 
provide an API to dispose the memory) ?

= In short, what must i code to do that ?

Re-Many thanks.

Fred
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-14 Thread Sven Barth 

On 14.03.2014 22:07, Fred van Stappen wrote:

  It's not a problem, as long as you provide an API to dispose the memory
  used by the returned PChar.
  The responsibility of calling this API is delegated
  to the application.

Yep, with pleasure,... but how to provide an API (and what do you mean
with provide an API to dispose the memory) ?

= In short, what must i code to do that ?


Inside your library you normally do this when creating a string result:

=== code begin ===

function InLibStringFunction: PChar; // of course declared as cdecl ;)
const
  MyString: AnsiString = 'Hello World'; // this string could also come 
frome somewhere else in your library

begin
  Result := GetMem(Length(MyString) + 1);
  Move(@MyString[1], Result, Length(MyString));
  Result[Length(MyString)] := 0;
end;

=== code end ===

Note: if your MyString is valid through the complete lifetime it could 
be used you can also use Result := PChar(MyString); instead, but if 
your string is e.g. a variable inside the function or a variable inside 
another function you must copy its content.


If you now allocated a PChar using GetMem you add this function as well 
and export it from the library:


=== code begin ===

procedure InLibFreeString(aStr: PChar);
begin
  FreeMem(aStr);
end;

=== code end ===

One could of course now extend the API with additional checks. E.g. so 
that you know that the string was really allocated by the library and 
not by e.g. the program using it. But maybe the heap manager already 
checks this, I don't know currently.


Regards,
Sven
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-14 Thread Fred van Stappen 
 Date: Fri, 14 Mar 2014 23:11:14 +0100
 From: pascaldra...@googlemail.com
 To: fpc-pascal@lists.freepascal.org
 Subject: Re: [fpc-pascal] Library.StringFunction() : PChar = NO
 
 On 14.03.2014 22:07, Fred van Stappen wrote:
It's not a problem, as long as you provide an API to dispose the memory
used by the returned PChar.
The responsibility of calling this API is delegated
to the application.
 
  Yep, with pleasure,... but how to provide an API (and what do you mean
  with provide an API to dispose the memory) ?
 
  = In short, what must i code to do that ?
 
 Inside your library you normally do this when creating a string result:
 
 === code begin ===
 
 function InLibStringFunction: PChar; // of course declared as cdecl ;)
 const
MyString: AnsiString = 'Hello World'; // this string could also come 
 frome somewhere else in your library
 begin
Result := GetMem(Length(MyString) + 1);
Move(@MyString[1], Result, Length(MyString));
Result[Length(MyString)] := 0;
 end;
 
 === code end ===
 
 Note: if your MyString is valid through the complete lifetime it could 
 be used you can also use Result := PChar(MyString); instead, but if 
 your string is e.g. a variable inside the function or a variable inside 
 another function you must copy its content.
 
 If you now allocated a PChar using GetMem you add this function as well 
 and export it from the library:
 
 === code begin ===
 
 procedure InLibFreeString(aStr: PChar);
 begin
FreeMem(aStr);
 end;
 
 === code end ===
 
 One could of course now extend the API with additional checks. E.g. so 
 that you know that the string was really allocated by the library and 
 not by e.g. the program using it. But maybe the heap manager already 
 checks this, I don't know currently.
 
 Regards,
 Sven

Yep, Sven, excellent and hyper clear.

Hum, i think that this code must go somewhere in wiki.
If you agree i will add it into fpc wiki.

Many thanks.

Fred.
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Re: [fpc-pascal] Library.StringFunction() : PChar = NO

2014-03-14 Thread Fred van Stappen 
 Note: if your MyString is valid through the complete lifetime it could 
 be used you can also use Result := PChar(MyString);

Hum, to be sure that i understand...

type
  TStringClass = class(TObject)
Name: AnsiString;   does not change
SomeText: AnsiString; / may change..
  end;

var
AStringClass : TStringClass;



function GetName: PChar;  cdecl ;
begin

result := PChar(AStringClass.Name);
end;

function GetSomeText: PChar;  cdecl ;
var
   MyString: AnsiString ;
begin

 MyString := AStringClass.SomeText ;
   Result := GetMem(Length(MyString) + 1);

   Move(@MyString[1], Result, Length(MyString));

   Result[Length(MyString)] := 0;

end;


Is it OK ?

Thanks.
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