FIELD
The FIELD statement creates a STRING type definition for a random-access file buffer.
Contents
Syntax
- FIELD [#]fileNumber&, fieldWidth1% AS variable1$[, fieldWidthN% AS variableN$]
Description
- fileNumber% is a file number used in the OPEN statement or a value from the FREEFILE function.
- Combined size of the fieldWidth% parameters must not exceed the LEN = recordsize in the RANDOM OPEN statement or a "FIELD overflow" error will occur.
- Variables are limited to STRING types. Use TYPE instead of FIELD if you want to use numerical values.
- Once a FIELD is defined in a statement, GET can read and PUT can write data without placeholders or variables.
- LSET, RSET, PRINT #, PRINT # USING, and WRITE # can be used to place characters in the file buffer before a PUT.
- All field definitions for a file are removed when the file is closed or RESET and all strings are set to null ("").
- Do not re-assign a field defined variable value or use it in an INPUT statement if you want the variable to remain a field.
Examples
Example: Comparing a TYPE definition with a FIELD string definition. Demo using a TYPE definition to create a file:
TYPE ClientType CName AS STRING * 30 '30 bytes Address AS STRING * 30 '30 bytes City AS STRING * 15 '15 bytes State AS STRING * 2 ' 2 bytes Zip AS STRING * 5 ' 5 bytes END TYPE ' total size = 82 bytes DIM Client AS ClientType RecordLEN = LEN(Client) 'find the size of each TYPE record OPEN "ADDRESS.DAT" FOR RANDOM AS #1 LEN = RecordLEN RESTORE ClientData 'restore to start of DATA record = 0 DO READ CName$, Address$, City$, State$, Zip$ 'read DATA IF CName$ = "END" THEN EXIT DO record = record + 1 'increment record number Client.CName = CName$ Client.Address = Address$ Client.City = City$ Client.State = State$ Client.Zip = Zip$ PUT #1, record, Client 'PUT by record number LOOP CLOSE #1 END ClientData: DATA "Bob White","104 Birdland Rd.","Bellview","PA","15236" DATA "Ward Cleaver","123 W. Beaver St.","Beaver","PA","15255" DATA "Elmer Fudd","45 Wabbit St.","Bethel Park","PA","15022" DATA "Wyley Coyote","33 Roadrunner Ave.","Clairton","PA","15122" DATA "Jim Morrison","19 Doorway Dr.","Belleview","PA","15236" DATA "END",0,0,0,0
Demo using the FIELD statement to read the file:
CONST NM = 30, AD = 30, CT = 15, ST = 2, ZC = 5 ' Define field and record lengths with constants. CONST RLEN = NM + AD + CY + ST + ZC ' OPEN "ADDRESS.DAT" FOR RANDOM AS #1 LEN = RLEN FIELD #1, NM AS CName$, AD AS Address$, CY AS City$, ST AS State$, ZC AS Zip$ FIELD #1, RLEN AS Clist$ 'define entire record GET #1, 1 'GET does not need a variable to read FIELD records! 'Read file for zip codes from 15230 to 15239 . DO WHILE NOT EOF(1) ZipCheck$ = Zip$ 'read zip codes IF (ZipCheck$ >= "15230" AND ZipCheck$ <= "15239") THEN Info$ = Clist$ PRINT LEFT$(Info$, 30) 'read name string PRINT MID$(Info$, 31, 30) 'read address string PRINT RIGHT$(Info$, 17) 'read city, state and zip code PRINT END IF GET #1 'simply GET reads each FIELD record after first LOOP CLOSE #1 END
See also
