RANDOM ACCESS FILES?

[jarychk]

I still am not so sure how to use random access files. I have made a few programs to use sequential files, often successfully, with much effort. What I have done with sequential files was maybe complicated; and maybe random access files could have been better to use instead - if I knew how.

I checked the JB tutorial and JB helpfile, and I believe I am beginning to understand the meanings of FIELD and RECORD. I gain not so much insight about more. Maybe a very very simple example program to just create, add information to , and view the file contents, could be useful or helpful. I am guessing that each record can be given an index number but I am not certain of this.

Something? Refer to tutorial or example program? Make an example program for a person to learn from?

[gaslouk]

Jul 12, 2024 1:03:20 GMT jarychk said:

I still am not so sure how to use random access files. I have made a few programs to use sequential files, often successfully, with much effort. What I have done with sequential files was maybe complicated; and maybe random access files could have been better to use instead - if I knew how.

I checked the JB tutorial and JB helpfile, and I believe I am beginning to understand the meanings of FIELD and RECORD. I gain not so much insight about more. Maybe a very very simple example program to just create, add information to , and view the file contents, could be useful or helpful. I am guessing that each record can be given an index number but I am not certain of this.

Something? Refer to tutorial or example program? Make an example program for a person to learn from?

Hi from beautiful Greece.

' Example Program for Random Access File Handling in Just BASIC
' This program creates, writes to, and reads from a random access file.

' Open the file for random access
OPEN "employees.dat" FOR RANDOM AS #1 LEN = 28

' Define the structure of a record
FIELD #1, 20 AS name$, 2 AS age$, 6 AS salary$

' Add records to the file
FOR RECORD = 1 TO 3
INPUT "Enter name: "; name$
INPUT "Enter age: "; age$
INPUT "Enter salary: "; salary$

' Ensure the data fits in the fields
name$ = LEFT$(name$ + SPACE$(20), 20)
age$ = RIGHT$("0" + age$, 2)
salary$ = RIGHT$("00000" + salary$, 6)

PUT #1, RECORD
NEXT RECORD

' Read and display the records
PRINT "Contents of the file:"
FOR RECORD = 1 TO 3
GET #1, RECORD
name$ = TRIM$(name$) ' Remove any trailing spaces
PRINT "Record "; RECORD
PRINT "Name: "; name$
PRINT "Age: "; VAL(age$)
PRINT "Salary: "; VAL(salary$)
PRINT
NEXT RECORD

' Close the file
CLOSE #1

END


Gaslouk.

[tsh73]

Fiew more points

1. It does supposed to work with records of the same structure. No similar records - no reason to use it
2. You should issue correct FIELD statement before actually using (reading/writing) file
3. You can use numeric fields, like "age". Field length would be number of digits (likely len(str$(age)))
4. it does truncate data if it not fit filed length, even if you do nothing about it.
   (so "' Ensure the data fits in the fields" part in example is somewhat redundant)
   In this example
   Enter name: very vey very long unusual name
Enter age: 101
Enter salary: 123456789

   you'll got
   very vey very long u
10
123456
   
5. Random access relies on each record having same size. So manually editing such file is generally BAD idea
6. You can get number of records in a file, here as lof(#1)/28 (28 is record size)
7. main point of it (RANDOM) that you do not have to read half of file (SEQUENTIALLY) to get say record 100. You just do GET #1, 100
8. Of cource you will get error if record 100 is not there. I've got "copy beyond end of file"

[jarychk]

gaslouk

The part I struggle to understand is the section, 'ensure the data fits in the fields'.

[jarychk]

Not yet at this level so maybe I should not ask yet -
but if a program uses random access file , and is used that a user adds for example , five records; can record number 2, or record number 3, be removed from the random access file later by the user?

each record is placed into the file one after the other, but then user might choose to delete one of the records (like, all of the fields' values of this record). Now the file would have a big empty spot. Must programmer compose code to cut down the true size of the file?

[plus]

Empty records can be removed by copying all records not empty to a new file, the old file deleted and then the new file renamed with the old name.

Another way is swapping records so the empty ones are placed at the end and new records are placed into the empty records before increasing the file size again. But all that file manipulation is ugly.

Best is to get all info out of file, do the processing from arrays and then store the info into a fresh new file. Just use files for storing.

b = b + ...