C-23

Lecture 23Lecture 23Version 1.0Version 1.0

More on Files More on Files (Part II)(Part II)

2Rushdi Shams, Dept of CSE, KUET, Bangladesh

Records in FileRecords in File

So far we have manipulated files So far we have manipulated files only with characters and strings.only with characters and strings.

What if you want to deal with What if you want to deal with numbers?numbers?

What if you want to deal with What if you want to deal with numbers/strings/characters all numbers/strings/characters all together?together?


The ProcedureThe Procedure

These are dissimilar data typesThese are dissimilar data types We will use structure to combine We will use structure to combine

these dissimilar data types into a these dissimilar data types into a single data structuresingle data structure

We will use fprintf ( ) to write them We will use fprintf ( ) to write them into fileinto file

We will use fscanf ( ) to read from We will use fscanf ( ) to read from filefile


Text & Binary FilesText & Binary Files

A text file contains only textual A text file contains only textual information like alphabets, digits information like alphabets, digits and special symbols and special symbols

In actuality the ASCII codes of these In actuality the ASCII codes of these characters are stored in text files characters are stored in text files

a binary file is merely a collection of a binary file is merely a collection of bytes bytes


Example of handling Example of handling binary filesbinary files

Remember the copy-paste program?Remember the copy-paste program? In that case, we handled only .TXT In that case, we handled only .TXT

filesfiles So, now we will modify the same So, now we will modify the same

program so that the program can program so that the program can handle binary files as well.handle binary files as well.

Don’t worry Don’t worry , it is almost the , it is almost the same program as that one!same program as that one!


The record I/O program that we did in The record I/O program that we did in an earlier section has two an earlier section has two disadvantages: disadvantages:

The numbers (basic salary) would The numbers (basic salary) would occupy more number of bytes- when the occupy more number of bytes- when the file is opened in text mode, each number file is opened in text mode, each number is stored as a character string. is stored as a character string.

If the number of fields in the structure If the number of fields in the structure increase writing structures using increase writing structures using fprintf( )fprintf( ), or reading them using , or reading them using fscanf( ), fscanf( ), becomes quite clumsy. becomes quite clumsy.


Efficient way to read/write Efficient way to read/write recordsrecords


fwrite ( &e, sizeof ( e ), 1, fwrite ( &e, sizeof ( e ), 1, fp ) ; fp ) ;

first argument is the address of the first argument is the address of the structure to be written to the disk structure to be written to the disk

second argument is the size of the second argument is the size of the structure in bytes structure in bytes

third argument is the number of such third argument is the number of such structures that we want to write at structures that we want to write at one time one time

argument is the pointer to the file we argument is the pointer to the file we want to write to want to write to


fread ( )fread ( )

If we have reached the end of file, If we have reached the end of file, since since fread( ) fread( ) cannot read anything, cannot read anything, it returns a 0. By testing for this it returns a 0. By testing for this situation, we know when to stop situation, we know when to stop reading. reading.

C-23

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