Initializing a file

[j.sreejit]

Hi friends,

I am new to file handling and i need some help.

How can i initialize a file with 100 empty records and then add new records as the user chooses to do so?

This is what I want to do:-

struct employee
{
char emp_dept[20];
char emp_name[20];
float salary;
};

filename: pers_data.dat

To begin with the file will contain 100 records, each will look like the foll:

emp_dept = "unassgined"
emp_name = ""
salary = 0.00

so first 5 records will be

unassgined            0.00
unassgined            0.00
unassgined            0.00
unassgined            0.00
unassgined            0.00

Is it possible to update and delete records without creating a new file?


Kindly help.

Thanks

[Kennedy]

fread(), fwrite(), fseek(), fopen() -- Check out the man pages on these, for a start.

[Salem]

First you open the file in binary mode using say
fp = fopen( "pers_data.dat", "rb" ); // for reading
fp = fopen( "pers_data.dat", "wb" ); // for writing
fp = fopen( "pers_data.dat", "r+b" ); // for reading and writing

If you have a variable say
struct employee me;

Reading and writing a record
if ( fread( &me, sizeof me, 1, fp ) == 1 ) // success
if ( fwrite( &me, sizeof me, 1, fp ) == 1 ) // success

Normally, when you read and write a record, the file automatically advances to the next record. So for example you can read the whole file in a simple loop.

To jump to a specific record (first record is record 0),
fseek( fp, recNum * sizeof me, SEEK_SET );

> Is it possible to update and delete records without creating a new file?
Yes, just have a field in your structure which means 'deleted' and then write that to the file.
Update is just an fseek followed by an fwrite

One final point, if you're doing lots of reading and writing, it's a good idea to do
fflush( fp );
after every fwrite.