Data Files• Allow us to store information permanently,

and access and alter information whenever necessary

• Types of data files– Stream-oriented (Standard) data files: Easier to

work with• Text file: consisting of consecutive characters• Binary file (unformatted data files): organizes data

into blocks. These blocks represent more complex data structure, such as arrays and structures

– System-oriented data files: closely related to the computer’s operating system

Opening and closing a data file• First establish a buffer area, where information

is temporarily stored while being transferred between the computer’s memory and the data fileFILE *ptvar;

• FILE is a special structure type that establishes the buffer area, ptvar is pointer (stream pointer or stream) that indicates the beginning of the buffer area.

Opening and closing a data file

• Data files must be opened before it is created or processed. This associates the file name with buffer area (i.e. with the stream)

• It also specifies how the data file will be utilized, as– Read-only file– Write-only file– Read/write file

Ptvar=fopen(file-name, file-type);

Opening and closing a data file• File name is a string, that specifies the name

(also location) of the file

• File-type must be one of the following string:– “r” =read only file– “w”=write only file. Destroy existing same name file– “a”=file for appending. New file created (if no file) – “r+”=both read and write file– “w+”=both read and write file. Destroy existing file.– “a+”=file for reading and appending. New file create

Opening and closing a data file

• fopen function returns a pointer to the beginning of the buffer area associated with file. (returns NULL is file does not exist)

• Data files must be closed at the end of the of the program

fclose(ptvar)

Reading and writing a data file

• putc(“a”, fpt): put a character into a data file• c=getc(fpt):read a character from a data file• fprintf(fpt,”%s”,custome.name): write the

value of a variable into a file• fscanf(fpt,”%s”, customer.name): read a

value from a file and store in a variable• feof(fpt):check whether end-of-file has been

reached or not

Reading and writing unformatted data file

• fwrite(&customer, sizeof(record),1,fpt): write a block of data stored in the variable customer, whose data type is record, in the file fpt 1 time

• fread(&customer, sizeof(record),1,fpt): read a block of data stored in the variable customer, whose data type is record, from the file fpt 1 time

Problems

• Take input from keyboard and store in a file

• Read from a file and display in the monitor

• Copy a file

• Encoding and decoding a file

• Create a file containing customer record

• Creating an unformatted data file containing customer record

Some more functions related to file

• fseek: seek a position and reposition the file pointer of a strean

• remove: delete a file

• ftell: return the current file pointer.Used to find the size of a file