FIELD
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The FIELD statement creates a STRING type definition for a random-access file buffer.
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