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RANDOM
RANDOM is used in an OPEN statement to read(GET) from or write(PUT) to a file.
OPEN Filename$ FOR RANDOM AS #1 [LEN = recordlength%]
- RANDOM is the Default mode if no mode is given in the OPEN statement.
- It creates the file if the legal file name given does NOT exist.
- As a RANDOM file, it can read or write any record using GET and/or PUT statements.
- Recordlength% is determined by getting the LEN of a TYPE variable or a FIELD statement.
- If no record length is used in the OPEN statement, the default record size is 128 bytes except for the last record.
- A record length cannot exceed 32767 or an ERROR Codes will occur!
- To determine the number of records in a file the records% = LOF \ recordlength%.
- When variable length strings are PUT into RANDOM files the record length must exceed the maximum string entry by:
- 2 bytes are reserved for recording variable string lengths up to 32767 bytes (LEN = longest + 2)
- 8 bytes are reserved for recording variable string lengths exceeding 32767 bytes (LEN = longest + 8)
- A serial communication port can also be opened for RANDOM in an OPEN COM statement.
Function that finds a RANDOM file's record number for a string value such as a phone number.
TYPE customer
age AS INTEGER
phone AS STRING * 10
END TYPE
DIM SHARED cust AS customer, recLEN
recLEN = LEN(cust) 'get the length of the record type
PRINT "RecLEN:"; recLEN
OPEN "randfile.rec" FOR RANDOM AS #1 LEN = recLEN
FOR i = 1 TO 4
READ cust.age, cust.phone
PUT #1, , cust
NEXT
CLOSE #1
RP = RecordPos("randfile.rec", "2223456789") 'returns 0 if record not found!
PRINT RP
IF RP THEN
OPEN "randfile.rec" FOR RANDOM AS #2 LEN = recLEN
GET #2, RP, cust
CLOSE #2
PRINT cust.age, cust.phone
END IF
END
DATA 59,2223456789,62,4122776477,32,3335551212,49,1234567890
FUNCTION RecordPos (file$, search$)
f = FREEFILE
OPEN file$ FOR INPUT AS #f
FL = LOF(f)
dat$ = INPUT$(FL, f)
CLOSE f
recpos = INSTR(dat$, search$)
IF recpos THEN RecordPos = recpos \ recLEN + 1 ELSE RecordPos = 0
END FUNCTION
Note: Random files can store records holding various variable types using a TYPE definition or a FIELD statement.
When not using a TYPE or fixed length strings, QB4.5 allows RANDOM files to hold variable length strings up to 2 bytes less than the LEN = record length statement:
_CONTROLCHR OFF
OPEN "myfile.txt" FOR OUTPUT AS #1: CLOSE #1: ' clears former file of all entries.
OPEN "myfile.txt" FOR RANDOM AS #1 LEN = 13 'strings can be up to 11 bytes with 2 byte padder
a$ = CHR$(1) + CHR$(0) + "ABCDEFGHI"
b$ = "ABCDEFGHI"
c$ = "1234"
PUT #1, 1, a$
PUT #1, 2, b$
PUT #1, 3, c$
FOR i = 1 TO 3
GET #1, i, a$
PRINT a$, LEN(a$)
NEXT
CLOSE
☺ ABCDEFGHI 11
ABCDEFGHI 9
1234 4
Note: The 2 byte file padders before each string PUT will show the length of a string for GET as ASCII characters. Padders will always be 2 bytes and strings up to the last one will be 13 bytes each no matter the length up to 11, so the file size can be determined as (2 + 11) + (2 + 9 + 2) + (2 + 4) or 13 + 13 + 2 + 4 = 32 bytes.