Question

consider this code:

program test;
uses crt;

var ptr1, ptr2:^integer;

begin
     new(ptr1);
     new(ptr2);
     writeln('ptr1: ',integer(@ptr1), ', ptr2: ', integer(@ptr2));
     ptr1:=ptr2;
     write('ptr1: ',integer(@ptr1), ', ptr2: ', integer(@ptr2));
     readln;
end.

second ‘write’ should give the same result for ptr1 and ptr2, but it gives (lazarus – free pascal):

ptr1: 4243456, ptr2: 4243472
ptr1: 4243456, ptr2: 4243472

In my opinion it should be:

ptr1: 4243472, ptr2: 4243472

I’m completely new to pointers. Did I understand something wrong?

Regards.

Answer 1

When you write @ptr1 you are not accessing the pointer, but creating a new pointer pointing to ptr. (pascal is not like perl with variable prefixes)

When you write

 writeln('ptr1: ',integer(ptr1), ', ptr2: ', integer(ptr2));
 ptr1:=ptr2;
 write('ptr1: ',integer(ptr1), ', ptr2: ', integer(ptr2));

, you get what you expected

(but it is better to use PtrInt instead of integer, because integer only works on 32 bit systems)