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