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50 lines
2.5 KiB
Text
50 lines
2.5 KiB
Text
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The '''INPUT''' file mode can only [[OPEN]] existing files with data in them for program [[INPUT (file statement)|INPUT]].
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{{PageSyntax}}
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:: OPEN filename$ FOR INPUT AS #filenumber%
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* If the filename does not exist, INPUT will create a program [[ERROR Codes|file error]]! Use [[_FILEEXISTS]] in QB64 to avoid errors.
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* The file number can be determined automatically by using a [[FREEFILE]] variable value.
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* Mode can use [[INPUT (file statement)|INPUT]] #, [[LINE INPUT (file statement)|LINE INPUT]] # or [[INPUT$]] to read the file data.
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* Use the [[EOF]] function to avoid reading data past the end of a file and creating an [[ERROR Codes|INPUT error]]!
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* Input file statements will use the same filenumber as the OPEN statement.
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* The INPUT mode allows the same file to be opened in another mode with a different number.
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''Example:'' Avoiding an INPUT mode or [[INPUT (file statement)|INPUT #]] read error using a FileExist function. QB64 can use the [[_FILEEXISTS]] function.
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{{CodeStart}} '' ''
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DIM Fdata$(100)
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INPUT "Enter data file name: ", datafile$
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IF FileExist%(datafile$) THEN
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D% = {{Cl|FREEFILE}}: count = 0
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{{Cl|OPEN}} datafile$ FOR {{Cl|INPUT (file mode)|INPUT}} AS #D%
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DO UNTIL {{Cl|EOF}}(D%)
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count = count + 1
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{{Cl|INPUT (file statement)|LINE INPUT}} #D%, Fdata$(count)
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IF count = 100 THEN {{Cl|EXIT}} DO ' don't exceed {{Cl|Arrays|array}} size!
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LOOP
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{{Cl|CLOSE}} #D%
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ELSE : PRINT "File not found!"
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END IF
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{{Cl|FUNCTION}} FileExist% (filename$)
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f% = {{Cl|FREEFILE}}
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{{Cl|OPEN}} filename$ FOR {{Cl|APPEND}} AS #f% ' check that file exists
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IF {{Cl|LOF}}(f%) THEN FileExist% = -1 {{Cl|ELSE}} {{Cl|CLOSE}} #f%: {{Cl|KILL}} filename$
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{{Cl|CLOSE}} #f%
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{{Cl|END FUNCTION}} '' ''
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{{CodeEnd}}
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: ''Explanation:'' The function opens the filename in [[APPEND]] mode to see if there is data in the file. It also creates the file if it did not exist. [[LOF]] will return 0 if the file is empty and cannot be read. In fact you can [[KILL]] the file if it is empty. If it is not empty then the function returns -1 and the existing file can be opened for INPUT and read by the program. [[_FILEEXISTS]] doesn't create any files.
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''See also:''
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* [[INPUT (file statement)|INPUT #]], [[LINE INPUT (file statement)|LINE INPUT #]], [[INPUT$]] {{text|(file input)}}
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* [[INPUT]], [[LINE INPUT]], [[INPUT$]] {{text|(keyboard input)}}
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* [[APPEND]], [[RANDOM]], [[OUTPUT]], [[BINARY]]
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* [[_FILEEXISTS]], [[_DIREXISTS]]
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{{PageNavigation}}
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