Datatypes Interoperability between Delphi and FPC.

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BSaidus:
Hello.
I'm trying to pass a Delphi(7) TStringList to a dll written in FPC and it do not works perhaps there is an Incompatibilities in the implimentation.
So I tried with pointers,
In delphi code:

--- Code: Pascal [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} --- // Delphi code var Lrec: TSomeREC ; // some record containing a pointer Llst: TStringList; begin .. Lrec.Adata = Pointer(Llst); // <== Assign list to pointer some_function_rec(Lrec); end; In Lazarus/FPC here is the code

--- Code: Pascal [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} --- // FPC code var Llst: TStringList; begin // .. Llst := TStringList(Arec.Adata); // <== Get the content of the pointer & assign it to Lis // .. Process then end; IT simply do not works.
During test, I constat that even with mode delphi, variables type string do not work. I replaced all strings with PChars but for the StringLists, it do not works.

Any solution for this ?
I ask because, I want to write a wrapper around TFPHttpClient to use in delphi, since it can handle different version of openssl, not like indy one.

Thank you.

Thaddy:
Better way is to pass the delphi stringlist text property as a pchar and the use () to set the freepascal text property

BSaidus:

--- Quote from: Thaddy on December 10, 2024, 09:48:39 am ---Better way is to pass the delphi stringlist text property as a pchar and the use () to set the freepascal text property

--- End quote ---
Hi Thaddy.
It is a good idea, but I think that PChar is limited in length to 255 when casting to string.
The StringList I want to use is for TFPHttpClient Post parameters, so what if the combination of all parameter is out of 255 ??

Thaddy:
Only shortstring has a limit. PChar can be as large as you want: high(ptruint)
There is one big difference with pascal strings: a pchar can not contain #0 values somewhere in the middle, but that is only a problem if you misuse a pchar to represent binary data.

Khrys:
PChar is not limited in length, but ShortString is (which String is an alias for unless {$H+} is used), so either add {$H+} to your Free Pascal code or explicitly use AnsiString when casting.

In any case, when interfacing between toolchains (such as FPC and Delphi) it's best to use simple scalar parameters while avoiding classes and managed types (including AnsiString), since the latter two aren't generally compatible.

So like Thaddy said it's probably best to use the Text property and pass the string as PChar:

--- Code: Pascal [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} ---// Delphiprocedure some_function(AData: PChar); stdcall; external 'fpc_lib.dll';// ...some_function(PChar(Llst.Text));

--- Code: Pascal [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} ---// FPC{$mode objfpc}{$H+} procedure some_function(AData: PChar); stdcall;var Llst: TStringList;begin Llst := TStringList.Create(); Llst.Text := AData; // Implicit cast to String, which is AnsiString under H+ // ...end;
Edit: Added explicit calling convention

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