How on TEXT FILES?

For work with a files, we need to definited a handle at first. We can do that in definition of cariables. File is a kind of file variable.

var f:text; { text file }

Hadle we connect to a file, which name we kno, its fo PC to know what kind of file we want to use. We get it to the command of assign. Next we will work with a file only with help of F variable.

Assign (f,'C:\subor.txt');

For next work we need to know, what we want to do ...read or write to the file. For any kind is a special commands of opening here.. For read, we use a ReSet ,and (handle) to the (For write we use ReWrite and handle.

ReSet(f); { for reading }
ReWrite(f); { for writing }

Next we use only a read and write ( Writeln or Readln).

Differences between Read and Write.

Write('Text na monitor');
Write(f,'Text do suboru'); { f is a handle of file... }

Read(i); { Read a variable from keyboard }
Read(f,i); { read from file }

ATTENTION:Write we use only for a file, which we have to pened before, ina command of ReWrite. Read only for files from a ReSet command.

If we want to read a file, program cannot know, where is a end of a file. For this, we have a EoF command (End of File), which we get to a condition of our cycle - while or repeat. Function of EoF is true, if we have the end of file in other, is a False.

ReSet(f);
while ( not( eof(f) )) do begin
ReadLn(f,s);
WriteLn(s);
end;

At the end, we need to end a work wih a file, so we CLOSE the file for save our progress.

Close(f);

Recapitulation.

1. ASSIGN - Connect a file with handle
2. RESET - Reading
REWRITE - Writing
3. WRITE - Writing to a file
READ - Reading from a file
EOF - Checking end of file with Read
4. CLOSE - End of connection

Two Examples

Example 1:
Open a file and write to it "Hello world".

program write_to_file;
var f:text;
begin
Assign(f,'c:\subor.txt');
ReWrite(f);
Write(f,'ahoj svet');
Close(f);
end.

Example 2:
Open a file, and write all o fit to the screen.

program for_reading_from_file;
var f:text;
s:string;
begin
Assign(f,'c:\subor.txt');
ReSet(f);

while ( not( eof(f) )) do begin
ReadLn(f,s);
WriteLn(s);
end;

Close(f);
end.

Annotation:

For work with more files, its good to have for every a handle, which we can use to work with it.
If we used ReWrite for an existing file,this file will be deleted and it will make a new, empty.
For check only for an end of a line, we can use a EOLN command.
Another command is APPEND. From a name we can know i tis for adding of text to the end of a file.
For work with a .dat files is using a variable of :file of xy" and the other commands, See in a next chapter.

<<Previous | Content | Next>>

Visitors: 1 943 235
Nameday: Dezider
Today: 11.02.2012, 06:17
Google Pagerank: 3 Counter naj.sk:

Joke in Slovak:
Pisomka z fyziky, zadanie prikladov, priklad cislo 3, ocelove telesa s hmotnostami
M1 a M2 sa zrazili, cest ich pamiatke