How to edit a specific line in a text file using Pascal - freepascal

Question

I am struggling to replace a specific line of text with my text from my program. So far, all I have is opening the file for editing...I tried searching on the internet but the closest one I could find was this: http://wiki.freepascal.org/File_Handling_In_Pascal. The page has everything about appending new texts under a line in an existing file and creating an entirely new file for adding texts into, but not for a specific line in an existing file...
var musicfile: TextFile;
AssignFile(musicfile, 'AlbumList.dat');
Append(musicfile);
WriteLn(musicfile, 'A text a want to replace line 5 with, but I dont know how to find line 5...');
Close(musicfile);

Answer 1

You can create new file and copy all the lines except the one you want to replace. Like this:
var musicfile: TextFile;
newfile: TextFile;
line: string[100]; // long enough to hold the longest line in the file
i: word; // counter for the lines
AssignFile(musicfile, 'AlbumList.dat');
AssignFile(newfile, 'AlbumList(1).dat'); // create new file
Reset(musicfile);
Rewrite(newfile); // open the new file for writing
i := 0 // we are at the 1st (index from zero) line
while not eof(musicfile) do begin
readln(musicfile, line); // read the line into a variable
if (i = 4) then // if we are at the 5th line, replace line
writeln(newfile, 'The string which should replace the 5th line')
else // just copy the line
writeln(newfile, line);
i := i + 1;
end;
Close(musicfile);
Close(newfile);

Answer 2

As someone who doesn't want to create a new file but wants to rewrite an old one I use TStringList (tested in lazarus btw):
var fileStrList:TStringList;
begin
fileStrList:= TStringList.Create; //creating the TStringList
try
fileStrList.LoadFromFile('AlbumList.dat'); //Loading file into TStringList
fileStrList[4]:='Text you want to replace line 5 with'; //rewriting line 5
fileStrList.SaveToFile('AlbumList.dat'); //saving rewritted TStringList to file
finally
fileStrList.Free; //freeing the TStringList !don't forget about this!
end;
end;