Delphi tutorial: Reading, Writing Files.

This has good information, and a search button at the bottom of the page

Please don't dismiss it because it isn't full of graphics, scripts, cookies, etc!

IGNORE ANY PERIODS (.) AT THE START OF ANY LINE

Simple File Handling.

This was first written long ago, originally in Delphi 1, for which it remains valid. In September 2002, I did the tutorial myself, using Delphi 2, making a few "tidies" here and there. If you find problems, do please let me know!

First: What do I mean by file handling? (For those of you who already know... be patient.. I'm only going to spend a about four paragraphs on this!)

A 'file' is something saved on a disc. Writing to a file is a bit like sending something to the printer. You have something in a variable, and you want it written down somewhere. The 'something' can be of any type- string, byte, integer, record. Continuing my analogy of printing as a way to understand writing to a file: Not only can you write to the file, but you can also put your something anywhere in the file that you want it, as if you were able to specify where on the page printing should occur. Often a file will be organised. The analogous piece of paper would have rows and columns marked on it, so you could say: "Write (it) in the second column of the third row."

The 'file handling as printing' analogy becomes a little strained when you learn that not only can you 'write' things on the 'paper', but if you overwrite something written earlier, a perfect 'erasure' occurs first.

The 'file handling as printing' analogy becomes even more strained when you turn to consider reading from a file. Not only can you write to a file, as discussed above, but you can also 'see' what has previously been put in any part of the file. Once everything else is in place, you have something like

function GetNthStringFromFile(bN:byte):string;
begin
GotoRecord(bN);
GetNthStringFromFile:=ReadStringFromFile;
end;

(Only function, begin, :=, string, byte and end in the above are built in elements of Delphi, by the way.)

Not only can you write to and read from files, but you can also delete them, rename them, move them, copy them etc.

So... that's what filehandling is. Now on to doing it...

for c1:=0 to 9 do WriteLineToFile(sSN[c1]);

if boFileOpen then begin
  closefile(df);
  boFileOpen:=false;
  end;

procedure TDD03f1.FormCreate(Sender: TObject);
type ByteFile=file of byte;
var df1,df2,df3:ByteFile;
c1,c2:byte;
sTmp:string;
function ReadTwo(var df:bytefile):string;(*'file of byte' unacceptable. You have to define a type, and use that*)
var sTmp:string;
    c1:byte;
begin
sTmp:='';
read(df,c1);
sTmp:=sTmp+chr(c1);
read(df,c1);
sTmp:=sTmp+chr(c1);
ReadTwo:=sTmp;
end;
procedure WriteTwo(sTmp:string);
var c1:byte;
begin
c1:=ord(sTmp[1]);write(df3,c1);
c1:=ord(sTmp[2]);write(df3,c1);
end;
begin
assignfile(df1,'In1.txt');
assignfile(df2,'In2.txt');
assignfile(df3,'Out.txt');
reset(df1);
reset(df2);
rewrite(df3);
for c1:=0 to 2 do begin
sTmp:=ReadTwo(df1);
WriteTwo(sTmp);
sTmp:=ReadTwo(df2);
WriteTwo(sTmp);
end;
closefile(df1);
closefile(df2);
closefile(df3);
end;

ByteFile=File of byte;
String28=string[28];

var
DD02f1: TDD02f1;
df:ByteFile;sSN:array [0..9] of string28;(*Score plus Name*)

{ByteFile=File of byte;  This now gone}
{String28=string[28];    This now gone}

var

DD02f1: TDD02f1;
df:file of byte;
sSN:array [0..9] of string[28];(*Score plus Name*)