Re: [fpc-pascal] pointer to char vs pchar

[Sven Barth via fpc-pascal]

Am 24.03.2023 um 15:04 schrieb Benito van der Zander via fpc-pascal:

why is a pointer to a char not a pchar (for type helpers)?


Because that's how helpers work in Delphi as well: The address operator 
has as a result an expression that allows the use of a helper for the 
raw Pointer type (no matter if $TypedAddress is enabled or not).


Regards,
Sven
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Re: [fpc-pascal] pointer to char vs pchar

[Michael Van Canneyt via fpc-pascal]

On Fri, 24 Mar 2023, Peter B via fpc-pascal wrote:


On 24/03/2023 14:29, Martin Frb via fpc-pascal wrote:

On 24/03/2023 15:04, Benito van der Zander via fpc-pascal wrote:
why is a pointer to a char not a pchar (for type helpers)? 


My guess: For the same reason that "p2" fails in the below. Distinct type.
May be assignment compatible, but a type of it's own.


My understanding is that pchars are supposed to be null terminated,
while the char in a pointer to a char might not be.


This is not quite correct.

By itself, a PChar can point to anything. 
Only if you typecast a valid ansistring to a pchar then the result of the

typecast is guaranteed to be null-terminated.


Michael.
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Re: [fpc-pascal] pointer to char vs pchar

[Peter B via fpc-pascal]

On 24/03/2023 14:29, Martin Frb via fpc-pascal wrote:

On 24/03/2023 15:04, Benito van der Zander via fpc-pascal wrote:
why is a pointer to a char not a pchar (for type helpers)? 


My guess: For the same reason that "p2" fails in the below. Distinct type.
May be assignment compatible, but a type of it's own.


My understanding is that pchars are supposed to be null terminated,
while the char in a pointer to a char might not be.
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Re: [fpc-pascal] pointer to char vs pchar

[Martin Frb via fpc-pascal]

On 24/03/2023 15:04, Benito van der Zander via fpc-pascal wrote:
why is a pointer to a char not a pchar (for type helpers)? 


My guess: For the same reason that "p2" fails in the below. Distinct type.
May be assignment compatible, but a type of it's own.

Imagine you had a different helper, with a different "toString" on 
pchar2, then which one should @char get?


program Project1;
{$Mode objfpc}{$H+} {$ModeSwitch typehelpers}
type
  pchar = ^char;
  pchar2 = ^char;

type TPcharHelper = type helper for pchar
  function toString(length: integer): string;
end;

function TPcharHelper.toString(length: integer): string;
begin
end;

var
  p: pchar;
  p2: pchar2;
begin
  p.toString(1);
  p2.toString(1);  // error
end.

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[fpc-pascal] pointer to char vs pchar

[Benito van der Zander via fpc-pascal]

Hallo,

why is a pointer to a char not a pchar (for type helpers)?


program Project1;
{$Mode objfpc}{$H+} {$ModeSwitch typehelpers}
type TPcharHelper = type helper for pchar
  function toString(length: integer): string;
end;

function TPcharHelper.toString(length: integer): string;
begin
  SetString(result, self, length);
end;

var c: char;
begin
  c := 'x';
  writeln((@c).toString(1)); //does not compile
  writeln(pchar(@c).toString(1));
end.

Bye,

Benito

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