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107 lines
4.2 KiB
Plaintext
107 lines
4.2 KiB
Plaintext
'''RANDOM''' is used in an [[OPEN]] statement to read([[GET]]) from or write([[PUT]]) to a file.
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{{PageSyntax}}
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:: OPEN Filename$ FOR RANDOM AS #1 [LEN = ''recordlength%'']
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* RANDOM is the Default mode if no mode is given in the [[OPEN]] statement.
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* It creates the file if the legal file name given does NOT exist.
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* As a RANDOM file, it can read or write any record using [[GET]] and/or [[PUT]] statements.
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* ''Recordlength%'' is determined by getting the LEN of a [[TYPE]] variable or a [[FIELD]] statement.
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:: [[STRING]] = 1 byte/character, [[INTEGER]] = 2 bytes, [[LONG]] = 4 bytes, [[SINGLE]] = 4 bytes [[DOUBLE]] = 8 bytes
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:: [[_BYTE]] = 1 byte, [[_INTEGER64]] = 8 bytes, [[_FLOAT]] = 10 bytes (so far)
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* If no record length is used in the [[OPEN]] statement, the default record size is 128 bytes except for the last record.
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* A record length cannot exceed 32767 or an [[ERROR Codes|error]] will occur!
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* To determine the number of records in a file the records% = [[LOF]] \ recordlength%.
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* When '''variable length strings''' are PUT into RANDOM files the record length must exceed the maximum string entry by:
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:: 2 bytes are reserved for recording variable string lengths up to 32767 bytes (LEN = longest + 2)
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:: 8 bytes are reserved for recording variable string lengths exceeding 32767 bytes (LEN = longest + 8)
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* A serial communication port can also be opened for RANDOM in an [[OPEN COM]] statement.
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''Example 1:'' Function that finds a RANDOM file's record number for a string value such as a phone number.
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{{CodeStart}} '' ''
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{{Cl|TYPE}} customer
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age {{Cl|AS}} {{Cl|INTEGER}}
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phone {{Cl|AS}} {{Cl|STRING}} * 10
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{{Cl|END}} {{Cl|TYPE}}
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{{Cl|DIM}} {{Cl|SHARED}} cust {{Cl|AS}} customer, recLEN
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recLEN = {{Cl|LEN}}(cust) 'get the length of the record type
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{{Cl|PRINT}} "Rec{{Cl|LEN}}:"; recLEN
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{{Cl|OPEN}} "randfile.rec" {{Cl|FOR...NEXT|FOR}} {{Cl|RANDOM}} {{Cl|AS}} #1 {{Cl|LEN}} = recLEN
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{{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} 4
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{{Cl|READ}} cust.age, cust.phone
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{{Cl|PUT}} #1, , cust
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{{Cl|NEXT}}
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{{Cl|CLOSE}} #1
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RP = RecordPos("randfile.rec", "2223456789") 'returns 0 if record not found!
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{{Cl|PRINT}} RP
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{{Cl|IF...THEN|IF}} RP {{Cl|THEN}}
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{{Cl|OPEN}} "randfile.rec" {{Cl|FOR...NEXT|FOR}} {{Cl|RANDOM}} {{Cl|AS}} #2 {{Cl|LEN}} = recLEN
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{{Cl|GET}} #2, RP, cust
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{{Cl|CLOSE}} #2
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{{Cl|PRINT}} cust.age, cust.phone
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{{Cl|END IF}}
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{{Cl|END}}
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{{Cl|DATA}} 59,2223456789,62,4122776477,32,3335551212,49,1234567890
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{{Cl|FUNCTION}} RecordPos (file$, search$)
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f = {{Cl|FREEFILE}}
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{{Cl|OPEN}} file$ {{Cl|FOR (file statement)|FOR}} {{Cl|INPUT (file mode)|INPUT}} {{Cl|AS}} #f
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FL = {{Cl|LOF}}(f)
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dat$ = {{Cl|INPUT$}}(FL, f)
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{{Cl|CLOSE}} f
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recpos = {{Cl|INSTR}}(dat$, search$)
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{{Cl|IF...THEN|IF}} recpos {{Cl|THEN}} RecordPos = recpos \ recLEN + 1 {{Cl|ELSE}} RecordPos = 0
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{{Cl|END FUNCTION}} '' ''
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{{CodeEnd}}
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:''Note:'' Random files can store records holding various variable types using a [[TYPE]] definition or a [[FIELD]] statement.
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''Example 2:'' When not using a [[TYPE]] or fixed length strings, QB4.5 allows RANDOM files to hold variable length strings up to 2 bytes less than the LEN = record length statement:
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{{CodeStart}} '' ''
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{{Cl|_CONTROLCHR}} OFF
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{{Cl|OPEN}} "myfile.txt" {{Cl|FOR...NEXT|FOR}} {{Cl|OUTPUT}} {{Cl|AS}} #1: {{Cl|CLOSE}} #1: ' clears former file of all entries.
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{{Cl|OPEN}} "myfile.txt" {{Cl|FOR...NEXT|FOR}} {{Cl|RANDOM}} {{Cl|AS}} #1 {{Cl|LEN}} = 13 'strings can be up to 11 bytes with 2 byte padder
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a$ = {{Cl|CHR$}}(1) + {{Cl|CHR$}}(0) + "ABCDEFGHI"
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b$ = "ABCDEFGHI"
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c$ = "1234"
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{{Cl|PUT}} #1, 1, a$
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{{Cl|PUT}} #1, 2, b$
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{{Cl|PUT}} #1, 3, c$
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{{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} 3
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{{Cl|GET}} #1, i, a$
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{{Cl|PRINT}} a$, {{Cl|LEN}}(a$)
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{{Cl|NEXT}}
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{{Cl|CLOSE}} '' ''
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{{CodeEnd}}
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{{OutputStart}}☺ ABCDEFGHI 11
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ABCDEFGHI 9
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1234 4
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{{OutputEnd}}
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: ''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.
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''See also:''
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* [[GET]], [[PUT]], [[FIELD]]
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* [[BINARY]]
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* [[SEEK]], [[SEEK (statement)]]
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{{PageNavigation}}
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