[SOLVED] How do you call a procedure given the procedure pointer in Pascal?

How do you call a procedure given the procedure pointer in Pascal?

Given an array of pointers where those pointers are to procedures and where they pass a single pointer passed to a procedure, how do you call the passed pointer?

procedure CallPointerProc(Proc : Pointer);
begin
  // ???????????
end;

The old DOS method was fairly simple but inline is not available on Windows port so couldn't even convert to ebx,esp, etc..:

inline(
    $89/$E3/               {mov bx,sp}
    $36/$FF/$1F/           {call dword ptr ss:[bx]}
    $83/$C4/$04);          {add sp,4}

Solution

In general, you should not pass a blank pointer but a type that describes the exact type of subroutine like parameters with their types and return type in case of a function.

Example on how to declares procedure or function types

type
  // A procedure with no parameters
  TProc = procedure;

  // A procedure that expexcts a string
  TStringProc = procedure(str: string);

  // A function that expects and returns a string
  TStringToStringFunc = function(str: string): string;

A function that expects a pointer to a procedure and calls it:

procedure CallPointerProc(Proc : TProc);
begin
  Proc();
end;

A function that expects a blank pointer, casts it to a procedure and then calls that:

procedure CallPointerProc(Proc : Pointer);
var
  TypedProc: TProc;
begin
  TypedProc := TProc(Proc);
  TypedProc();
end;

Demo code that works with both definitions of CallPointerProc above. Note that we use the @ symbol to get the address of a defined procedure or function.

procedure Demo;
begin
  Writeln('Hello World');
end;

begin
  CallPointerProc(@Demo);
  Readln;
end.