RANDOM
RANDOM is used in an OPEN statement to read(GET) from or write(PUT) to a file.
Syntax
- 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 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.
Example 1: 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$) IF recpos THEN RecordPos = recpos \ recLEN + 1 ELSE RecordPos = 0 END FUNCTION
- Note: Random files can store records holding various variable types using a TYPE definition or a FIELD statement.
Example 2: When not using a TYPE or fixed length strings, QB4.5 allows RANDOM files to hold variable length strings up to 2 bytes less than the LEN = record length statement:
_CONTROLCHR OFF OPEN "myfile.txt" FOR OUTPUT AS #1: CLOSE #1: ' clears former file of all entries. OPEN "myfile.txt" FOR RANDOM AS #1 LEN = 13 'strings can be up to 11 bytes with 2 byte padder a$ = 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.
See also:
