Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mcvax!unido!pbinfo!corona!pgcomp
From: pgcomp@pbinfo.UUCP (Projektgr. Uebersetzerbau)
Newsgroups: comp.lang.pascal
Subject: Re: Pointers..
Message-ID: <537@corona.pb>
Date: 30 May 89 09:02:43 GMT
References: <3398@westfort.UUCP>
Organization: Uni-GH Paderborn, Germany
Lines: 62

In article <3398@westfort.UUCP>, dragon@westfort.UUCP (The Mystic) writes:
] 
]         I managed to get pointers working w/ files, yet for some reason when I 
] come back to the file, it's all garbage.. I realize that the pointers were for 
] memory vars only, but this program created a disk file as I specified in my 
] assign command.. Perhaps an example..
] 
] Program testheap;
]  
] uses dos,crt;
]  
] Type
]    boardtype=^boardrec;
]    boardrec=record
] name:string[20];
] age:integer;
] end;
] Var
]   msgbase:boardtype;
]   messagebase:file of boardtype;
]  
] procedure getest;
] begin
]  clrscr;
]   write('Enter Your Name: '); readln(msgbase^.name);
]   write('Enter Your Age.: '); readln(msgbase^.age);
]   assign(messagebase,'c:\pascal\testfile.dat');
]   {$I-} reset(messagebase); {$I+}
]      if ioresult<>0 then rewrite(messagebase);
]   write(messagebase,msgbase);
]   close(messagebase);
] end;
]  
] procedure readtest;
] begin
]   assign(messagebase,'c:\pascal\testfile.dat');
]   writeln;
]   {$I-} reset(messagebase); {$I+}
]      if ioresult<>0 then rewrite(messagebase);
]   read(messagebase,msgbase);
]   with msgbase^ do begin
]      writeln('Your name is: ',name);
]      writeln('Your Age is.: ',age);
]      delay(5000);
]    close(messagebase);
]   end;
] end;
]  
] begin getest; readtest; end.
] 
] If I take out the getest from the routine, after I've run other programs, it 
] brings up garbage... Why?


Didn't you remember the difference between pointers and variables ?
You declared msgbase as a pointer to boardrec, but you didn't allocate 
(* new(msgbase) *) any memory space for holding an element of type boardrec. 
Thus any operation with msgbase must fail due to writing in nonallocated 
memory space.

			   thomas roemke
			   (tt)