Address of function in typeless pointer constant
lazarus / 62-General

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TCH · 2021-10-14 21:00

I have a small program:Code: Pascal  [Select][+][-]window.onload =
function(){var x1 = document.getElementById("main_content_section");
if (x1) { var x = document.getElementsByClassName("geshi");for (var i
= 0; i program x; function kecske(a: integer): integer; cdecl;begin  
    kecske := a + 8;end; var ptr: Pointer =
Pointer(@kecske); beginend.fpc x.pasCode: [Select]x.pas(8,36) Error:
Illegal expressionIf i change the var to const, the result is
identical. How can i store a function's address to a constant or an
initialized variable as an untyped pointer?

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howardpc · 2021-10-14 22:59

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
pointerEx; {$mode objfpc} function kecske(a: integer): integer;
cdecl;begin  kecske := a + 8;end; var  pKecske: Pointer =
@kecske; beginend.This compiles OK for me.

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TCH · 2021-10-15 08:09

Yeah, that worked for me too, but unfortunately it did not worked in
my real case. My example program was incomplete. This was more like
what i wanted to accomplish:Code: Pascal  [Select][+][-]window.onload
= function(){var x1 = document.getElementById("main_content_section");
if (x1) { var x = document.getElementsByClassName("geshi");for (var i
= 0; i program x; type        TProc = procedure; cdecl;        TKecske
= function (a: integer): integer; cdecl;        PPointer =
^Pointer; var Func: TProc; function kecske(a: integer): integer;
cdecl;begin        kecske := a + 8;end; const        pKecske: Pointer
= @kecske;        pFunc: Pointer = @Func; procedure set_it1(src:
Pointer; dst: PPointer);begin        dst^ := src;end; begin       
set_it1(pKecske, @pFunc);        WriteLn(TKecske(pFunc)(8));end.But in
the meantime, i figured it out, the catch was casting the pointer to
ppointer. Thanks for helping.

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howardpc · 2021-10-15 10:11

I think it is generally better practice to use typed pointers, or if
you have to use an untyped pointer cast it to the correct type:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
pointerEx; {$mode objfpc} type   TFunc = function(b: Integer):
Integer; cdecl; function kecske(a: integer): integer; cdecl;begin 
kecske := a + 8;end; var  pKecske: Pointer = @kecske; begin 
WriteLn(TFunc(pKecske)(8);  ReadLn;end.

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TCH · 2021-10-15 10:25

I have to work with different type of procedures and functions and
store their addresses in a common list, so i only can store them as
untyped pointers; usage is done with casting of course.