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Languages :: Pascal :: passing pointer to a procedure
By: VB guy Canada  Date: 06/01/2003 00:00:00  English  Points: 50 Status: Answered
Quality : Excellent
let's say u have a pointer pointing to a record which stores info entered by the user. all the info can be easily accessed with use of linked lists, but how would u pass this data (the record) to a procedure? if it helps, below is my incomplete program where im trying to implement this. the idea is that once all the user-entered data has been collected, it will copy all the info to a DAT file, output the info as entered by user, and then move onto one of two procedures. in either one, i need to access the records stored in the main program, but dont know how to do this.



program linksys1;
uses crt;

type CustPtr = ^CustRec;
CustRec = record
FName, LName : string[13];
phone, fax : string[12];
address : string[20];
city, prov, pcode : string[15];
Prev, Next : CustPtr;
end;

{---------------------------------------------------------------------------}
procedure postalcodes (first,current,prev : custptr; var fhfile:text);
var found : custptr;

begin
new (first);
current := first;

writeln ('YAAAA');
writeln (current^.fname);
writeln (current^.lname); readkey;


end;

{---------------------------------------------------------------------------}
procedure areacodes (first,current,prev : custptr; var fhfile:text);

begin

end;

{---------------------------------------------------------------------------}



var first,current,prev : CustPtr;
creply : char;
fhfile : text;


begin
clrscr;
assign (fhfile, 'ClientInfo.dat');
rewrite (fhfile);
append (fhfile);
first := nil;


repeat
clrscr;
if (first=nil) then
begin
new (first);
current := first;

write ('Enter the first name: ');
readln (current^.fname);
write ('Enter the last name: ');
readln (current^.lname);
write ('Enter the phone #: ');
readln (current^.phone);
write ('Enter the fax #: ');
readln (current^.fax);
write ('Enter the street address: ');
readln (current^.address);
write ('Enter the city name: ');
readln (current^.city);
write ('Enter the province name: ');
readln (current^.prov);
write ('Enter the postal code: ');
readln (current^.pcode);

end
else
begin
prev := current;
new (current^.next);
current := current^.next;

write ('Enter the first name: ');
readln (current^.fname);
write ('Enter the last name: ');
readln (current^.lname);
write ('Enter the phone #: ');
readln (current^.phone);
write ('Enter the fax #: ');
readln (current^.fax);
write ('Enter the street address: ');
readln (current^.address);
write ('Enter the city name: ');
readln (current^.city);
write ('Enter the province name: ');
readln (current^.prov);
write ('Enter the postal code: ');
readln (current^.pcode);

new (current^.next);
current^.next := nil;
end;

writeln('');
write('Are there any more customers? (y/n)');
readln (creply);


until (creply='n') or (creply='N');

{Write to file}
current := first;

repeat
writeln (fhfile, current^.fname);
writeln (fhfile, current^.lname);
writeln (fhfile, current^.phone);
writeln (fhfile, current^.fax);
writeln (fhfile, current^.address);
writeln (fhfile, current^.city);
writeln (fhfile, current^.prov);
writeln (fhfile, current^.pcode);
writeln (fhfile, '');

current := current^.next;

until (current=nil);
writeln (fhfile, 'ENDCHECK');
{Output to screen}
current := first;

repeat
writeln (current^.fname);
writeln (current^.lname);
writeln (current^.phone);
writeln (current^.fax);
writeln (current^.address);
writeln (current^.city);
writeln (current^.prov);
writeln (current^.pcode);
writeln ('');
current := current^.next;

until (current=nil);



{ clrscr;
writeln ('Make a choice: ');
writeln ('P.) Read through the record and print all records with postal codes starting with L or M');
writeln ('A.) Read through the record and print all records with area codes starting with 705');
write ('Enter your choice: '); readln (creply);

if (creply='P') or (creply='p') then
begin
postalcodes (first, current, prev,fhfile);
end
else if (creply='A') or (creply='a') then
begin
areacodes (first, current, prev, fhfile);
end; }

current := first;
writeln ('YAAA');
writeln (current^.fname);
writeln (current^.lname);
readkey;



current := first;
{Dispose record}
while current^.next <> nil do
begin
first := current^.next;
dispose(current);
current := first;
end;


readkey;
close (fhfile);

end.



any response would be appreciated. thanx.
By: monange Date: 07/01/2003 07:08:00 English  Type : Comment
This might be enough of a start. All it does is print out the postal codes that start with L for you but should give you the idea.

Not tested and no guarantee.

Oh, and inside a procedure try and make the names of any parameters inside a procedure a different name to that passed to it, eg


procedure process_data(first_no, second_no : integer);
begin
total := first_no + second_no;
end;

and when you call it.

process_data(number_one, number_two : integer);




procedure postalcodes (first : custptr; );
begin
while first<> nil do
begin
if first^.pcode[1] = 'L' then
begin
writeln (first^.fname);
writeln (first^.lname);
writeln (first^.phone);
writeln (first^.fax);
writeln (first^.address);
writeln (first^.city);
writeln (first^.prov);
writeln (first^.pcode);
writeln ('');
end;
first := first^.next;
end;
end;
By: VGR Date: 08/01/2003 07:59:00 English  Type : Comment
note also that "first" is not disposed of in your code above.

Then I would also pass the record variable's reference as a VAR parameter (just good practice, no impact ont he code I guess)

And last, I already use records' files all the time. You should use a file of typerecord and just do Write(fileof,yourrecord) and read(fileof, yourrecord)

it's easier
By: VGR Date: 08/01/2003 20:02:00 English  Type : Answer
correction to the above : of course as you have a linked list, you can't just write records the way I wrote. Stick with your loops. You could still use a file of recordtype, write each record wholly, but need to have an indicator "this is the follow-up of the current list", and you would ignore pointers' values when reading back

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