The document discusses how to utilize text files in Delphi programming to manage external information, highlighting the process of reading, manipulating, and displaying data from text files. It explains critical steps such as checking file existence, reading lines, employing loop structures, and extracting data. It emphasizes using the end-of-file and end-of-line markers for processing the data effectively.

1. 1
Introduction: Text files

2. 2
 Text files is a means of making use of external information in
a Delphi project.
 You can use the information and manipulate it into data.
 For example take a look at the following data from a text file:
Mr
De Swart J.P.
Mrs
Malima S.
Dr
Davids W.S.
Mr
Aldridge D.
Text File

3. 3
 The information in the text file makes NO sense.
 With the help of a Delphi program we can luckily
fix this.
 The program will assist us to change the DATA
(from the text file) into usable information.
Text File

4. 4
 Fist you need to create a variable name that you
will use in your program to indicate that you are
working with a text file;
procedure TForm1.btnReadFromFileClick(Sender:
TObject);
Var
MyFile : TextFile;
Create a variable name

5. 5
 When you start to work with text files in a
programming language it is very important to
always check if the specific text file does exist.
if FileExists('Guests.txt') = False then
begin
ShowMessage('The file does not exist');
Application.Terminate;
end;
Test if the file exists
Test for file existence
Always give a user
friendly message
Exit program if file
does not exist.

6. 6
 Next you need to introduce the external file
(Guests.txt) to the internal file (MyFile) because
from now on you will refer to the internal file
when you want to work with the data in the text
file.
AssignFile(MyFile,'Guests.txt');
External file meets Internal file

7. 7
 In every text file there are two types of markers
that we will make use of when we want to use
the data from the file.
 The first marker is the end of file (EoF) marker.
This marker will indicate where the ended.
 The second marker is the end of line (eol)
marker. This will indicate the end of each line in
the text file;
Different markers in a text file

8. 8
ZA1,Felidae,Acinonyx jubatus,Cheetah,2,1,50,VUeol
ZA2,Felidae,Caracal caracal,Caracal,2,2,36,LEeol
ZA5,Felidae,Felis nigripes,Black-footed
cat,2,0,36,VUeol
ZA9,Felidae,Felis silvestris,Wildcat,3,3,36,LEeol
ZB2,Felidae,Leptailurus serval,Serval,3,5,80,LEeol
ZB5,Felidae,Panthera pardus,Leopard,3,3,700,LEeol
ZB6,Felidae,Panthera leo,Lion,4,2,800,Vueol EoF
Example of data in a text file

9. 9
 Lets say the reading glasses, in the previous
slide, will simulate where the person, that last
opened the text file, stopped working.
 This means we need to get the reading glasses
back to the top of the file to read the data from
the beginning of the file.
Example of data in a text file

10. 10
 The next step will then be to write the code to
open the text file and to put the reading glasses
at the beginning of the file ready to start
reading the data from the beginning of the file.
We do that with the following code:
Reset(MyFile);
Open and ready the file

11. 11
 Next to make sure that you read everything
from the text file you will need some kind of a
loop structure.
 We know of two types of loops:
 For loop – number of iterations is known.
 While loop – number of iterations is unknown.
 Which loop structure will we make use of?
Loop structure for reading through
the file

12. 12
 Great! We will need a WHILE loop structure.
 What will my condition be? Look at the example again and see if
you can identify the loop condition.
ZA1,Felidae,Acinonyx jubatus,Cheetah,2,1,50,VUeol
ZA2,Felidae,Caracal caracal,Caracal,2,2,36,LEeol
ZA5,Felidae,Felis nigripes,Black-footed cat,2,0,36,VUeol
ZA9,Felidae,Felis silvestris,Wildcat,3,3,36,LEeol
ZB2,Felidae,Leptailurus serval,Serval,3,5,80,LEeol
ZB5,Felidae,Panthera pardus,Leopard,3,3,700,LEeol
ZB6,Felidae,Panthera leo,Lion,4,2,800,Vueol EoF
Loop structure for reading through
the file

13. 13
 The code that will be responsible for looping through
the file is:
while Not Eof(MyFile) do
begin
end;
 This code simply says: while it is NOT the end of the
file do what ever is going to follow.
Loop structure for reading through
the file

14. 14
 Now we need to read a line from the text file
before we can start to manipulate the data.
Readln(MyFile,sLine);
 The sLine is a string variable that was locally
assigned.
 This variable will serve as a temporary storage
bucket for the line that was red from the text
file.
Read data from file into
variable

15. 15
 You can take the data from the variable sLine
and manipulate it in any way that will assist you
to solve your problem.
 On the next few slides we will look at possible
scenarios in getting the data from sLine so that
it will serve our purpose.
Read data from file into
variable

16. 16
 Example of text file data. Every line contains a different variable information:
Peet
Coetzee
Nellie
Roos
Thabo
Mzinkizi
While Not EoF(MyFile) do
begin
Readln(MyFile,sLine);
sName := sLine;
Readln(MyFile,sLine);
sSurname := sLine;
End;
Extract data from the variable

17. 17
 Example of text file data: Delimited text file (the delimited character can be
any character, in this case it is an *):
Keagan*Foordt*45612378
Meagan*Ranch*785623402
Ryan*Keet*12567958
While Not EoF(MyFile) do
begin
Readln(MyFile,sLine);
sName := Copy(sLine,1,Pos(‘*’,sLine)-1;
Delete(sLine,1,Pos(‘*’,sLine);
sSurname := Copy(sLine,1,Pos(‘*’,sLine)-1;
DeleteCopy(sLine,1,Pos(‘*’,sLine);
sNumber := sLine;
end;
Extract data from the variable

18. 18
 sName := Copy(sLine,1,Pos(‘*’,sLine)-1;
Understand the coding:
String
variable
Locate the
delaminated
character(*) in
the data
Copy everything from the
fist character to just
before the delaminated
character.
Do NOT copy the
*

19. 19
 Delete(sLine,1,Pos(‘*’,sLine);
 sNumber := sLine; last bit of remaining info in sLine can
be red directly into the variable
Understand the coding:
Delete everything from the first character to
the delimited character (Including this
character)

20. 20
 There are many different ways to display the data
from our program, it all depends on the question.
 For example you can use a rich edit:
redOutput.Lines.Add(sTitle +' '+sSurname);
end;
closeFile(MyFile);
 The CloseFile is to make sure that you close your text file
after you are finished working in it.
Output and close file