Lecture 12 - Pascal Programming (Part VI)

File Processing
pascal provides a simple set of functions reading and writing data into external storage devices. A collection of data written into a storage is called a file. There are two types of files used in Pascal. All files require an internal identifier which can be declared as below.

Text Files
These are a series of characters written into a file. These files are human readable and uses ASCII text characters.

VAR
Myfilel : TEXT; { identifier for a text file )

Binary Files
These are blocks of data that is written into a file. These files cannot be displayed without using an appropriate program to read and display them.

VAR
DataFilel : FILE of integer;
DataFile2 : FILE of StuCentRecord; { identifier for a binary file )

File Handling Functions

Assign( DataFilel, 'Stud.Dat') - This function is used to assign an internal file identifier to an external filename.

Reset(DataFilel ) - Opens the file for reading data

Rewrite(DataFilel) - reates a new file for writing data. lf used on existing one the data get erased.

Append(DataFilel ) - Opens an existing file for adding new records to the bottom.

Close(DataFilel ) - Closes the file.

Write(DataFilel,MyData) - Writes a record to the current position of the file.

Read(DataFilel,MyData) -  Read the current record from the file.

Seek(DataFile1,5) - Move the file pointer to the 5th record on the file.

EOF(DataFilel ) - Returns True if you have reached the end of the file.

Writeln and Readln also can be used in reading and writing into text files. Writeln writes a newline characters to make the file more readable when displayed.

Read 5 Student's Details and Write them into a new binary File

PROGRAM Example13;
TYPE
StudType = RECORD
ld . integer;
Name . String[2O];
END;
VAR
File'l : FILE of StudType;
StudTable : ARRAYI1..5] of StudType; {Create an array of 5 records}
X . integer; iCounter variable)

BEIGN
{Get details from the user to enter into the file}
FOR X:='1 TO 5 Do
BEIGN
Writeln('Student -', X,'--------------');
Write('Enter lD: ');
Readln( StudTable[X]. ld);
Write('Name:');
Readln( StudTable[X]. Name);
Writeln;
END;

Assign( File1,'C:\temp\Students.dat');
Rewrite( Filel);

FOR X:=1 TO 5 DO
Write( File'l, StudTable[X] ); { Write 5 Records into the File }

Close( Filel );

This program copy one text file to another. Both file names are entered through keyboard.
PROGRAM Example14;
VAR
lnFile, OutFile :Text;
Filenamel, Filename2 : String[20];
Ch : Char

BEIGN
Write('Enter lnput File Name');
Readln ( Filenamel );

Write('Enter Output File Name');
Readln( FileName2 );
Assign( InFile, Filenamel );
Assign( OutFile, Filename2 );

Reset( lnFile );
Rewrite( OutFile );
IF lnFile=Nil OR OutFile=NIL THEN
Writeln('File Open Error')
ELSE
BEGIN
WHILE NOT EOF( InFile )DO
BEGIN
Read( lnFile, Ch );
Write( OutFile, Ch );
END;
Writeln(' File Successfully Copied ')l
END;
Close( InFile );
Close( OutFile );
END