Delphi for loops and StringList Errors - delphi

Question

Ok guys, I've been trying to find out every possible mistake i'm making but I give up... I need help! What I'm writing is an app to manage rentals for my job and when the date is past, my app removes the name from 2 text files. I wrote 3 little functions(procedures) to make this work. Here:
This one loads from dates.dat file and remove the line containing the name of the employee.
procedure remDate(emp: String);/// Removes employee from date file
var
pos1, i: integer;
dateList: TStringList;
begin
dateList:=TStringList.Create;
dateList.LoadFromFile('Data\dates.dat');
for i:=0 to dateList.Count-1 do begin
pos1:=AnsiPos(emp, dateList[i]);
if pos1<>0 then begin
dateList.Delete(i);
dateList.SaveToFile('Data\dates.dat');
end;
end;
dateList.Free;
end; //eo remDate
This one removes the line containing the employee name from the perm.dat file.
procedure remPerm(emp: String);/// Removes employee from perm file
var
pos1, i: integer;
permList: TStringList;
begin
permList:=TStringList.Create;
permList.LoadFromFile('Data\perm.dat');
for i:=0 to permList.Count-1 do begin
pos1:=AnsiPos(emp, permList[i]);
if pos1<>0 then begin
permList.Delete(i);
permList.SaveToFile('Data\perm.dat');
end;
end;
permList.Free;
end; //eo remPerm
This one sticks those together. The isDue is a simple function that compares 2 dates and returns a TRUE if date is today or is past.
procedure updatePerms;
var
empList: TStringList;
i: integer;
begin
empList:=TStringList.Create;
empList.LoadFromFile('Data\employes.dat');
for i:=0 to empList.Count-1 do begin
if isDue(empList[i]) then begin
remDate(empList[i]);
remPerm(empList[i]); (*) Here is where the error points.
end;
end;
empList.Free;
end;
The error I get is when it gets to remPerm in the updatePerms procedure.(*)
I get a EStringList Error, out of bound (#). Figured out with many tries that it only happens when an employee's due date is today. Please comment if you need more info!
Thanks in advance, any help is really appreciated!

Answer 1

The problem is that you are using a for loop. The end point of a for loop is only evaluated once when the loop is entered. At that point you may have 100 items, but once you start deleting there will be less. This will then result in a list index out of bounds error.
The simple fix is to reverse the for loop:
procedure remDate(emp: String);
/// Removes employee from date file
var
pos1, i: integer;
dateList: TStringList;
begin
dateList := TStringList.Create;
dateList.LoadFromFile('Data\dates.dat');
for i := dateList.Count - 1 downto 0 do
begin
pos1 := AnsiPos(emp, dateList[i]);
if pos1 <> 0 then
begin
dateList.Delete(i);
dateList.SaveToFile('Data\dates.dat');
end;
end;
dateList.Free;
end; // eo remDate
This will work if the employee occurs more than once.
However if the employee does only occur once, you can use break to exit from the loop early:
procedure remDate(emp: String);
/// Removes employee from date file
var
pos1, i: integer;
dateList: TStringList;
begin
dateList := TStringList.Create;
dateList.LoadFromFile('Data\dates.dat');
for i := 0 to dateList.Count - 1 do
begin
pos1 := AnsiPos(emp, dateList[i]);
if pos1 <> 0 then
begin
dateList.Delete(i);
dateList.SaveToFile('Data\dates.dat');
Break; // <-- early exit
end;
end;
dateList.Free;
end; // eo remDate
Another solution is to use a while loop.