Hairy Pixels via fpc-pascal said on Thu, 22 Jun 2023 20:23:13 +0700 >I've forgotten entirely, what does subscripting a pointer do in >Pascal? p[0] returns 100 but after that garbage. Seems like a c-style >array which doesn't feel right in the language. > >var > i: Integer; > p: PInteger; >begin > p := @i; > p^ := 100; > writeln(p[0]); > writeln(p[1]); > writeln(p[2]); > >Regards, > Ryan Joseph
I don't do much with Pascal pointers, but it looks to me like you: * Set p to the address of i * Set the contents of p to 100 * Read the contents of p, which of course would be the value of i, 100 * Read the contents of p+1, which would be one integer width away on the stack, and has not been assigned to anything. So what you report is exactly what I'd expect to happen. If p were pointing to the first element of an array of integer that had been initialized, it would have worked the way you intended. p[1] is undefined, but if I had to guess, the way most compilers seem to work, I'd say it would be one integer width of the value of p[0], which is the address of i. If my supposition is correct, by modifying the contents of p[1] and maybe some other elements of p, you could write some pretty interesting self-modifying code. But don't do that. SteveT Steve Litt Autumn 2022 featured book: Thriving in Tough Times http://www.troubleshooters.com/bookstore/thrive.htm _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
