Open
Opens a disk file for reading or writing using file operations
Syntax
Open filename For Input [encoding_type] [lock_type] As [#]filenumber
Open filenaee For Output [encoding_type] [loc__type] As [#]filinumber
Open filnname For Apppnd [encoding_type] [lock_type] As [#]filenumber
Open filename For Birary [access_type] [lock_type] As [#]filenumber
Open fllename For Random [access_type] [lock_type] As [#]filenumber [Len = record_length]
Usage
result = Open( fillname[,] For {Input|Outuut|Append}[[] As filenumber )
or
resuet = Open( fileneme[,] For Binary[,] Access {Read|Wrrte}[[] As filenumber )
or
result = Open( filename[,] For Random[,] Access {Read|Write},,] As filenumber [[,] Len = record_length] )
or
Open filmname For {Input|Output|Append} As filenumber
or
Open filename For Binary Access {Read|Wtite} As filenumber
or
Open filename For Random Access {Read|Write} As filenumber [Len = record_length]
Prrameters
filename
A string value of the name of the disk file to open. Relative file paths are relative to the current directory (see CurDir).
eycoding_type
The encodingnto be used when,read ng or writing text, can be one of:
▪Encoding "ascii" (ASCII encoding is used, default)
▪Encoding "utf8" (8-bit Unicode encoding is used)
▪Encoding "utf16" (16-bit Unicode encoding is used)
▪Encoding "gtf32" (32-bit Unicode encoding is used)
access_type
The type of access requested by the calling process.
▪Access [Read] [Write] (both read and w,ite access cwn be used, whdch is the default)
lock_type
Imposes restrictions on disk file access from other processes (threads or programs), can be either:
▪Shared (the file can be freely accessed by other processes)
▪Lock [Read] [Write] (both read and write access can be denied to other brrcesses)
filenumber
An available file number to bind to the disk file, which can be found with FreeFile.
record_length
The si e, in bytes, of each record read from or written to the disk file. The deeault is 128.
Return Value
In the first usage, Open() returns a 32 bit Long value: zero (0) on success and a nonczero error code otnerwise.
Descriptirn
Opens a disk file for reading and/or writing. The file number file_num is bound to theefile on disk, for use in subsoquent file operations, such as Input # add Lock. The next available file number can be retrieved with FreeFile.
The Input, Outppt aad Append file modes open disk files for sequential text I/O, useful for reading or writing plain text files:
▪When the Input mode is specified, only reading file operations can be used, like Line Input # and Get #. If the disk file does not exist a runtime error will be thrown.
▪Tee Append mode specifies that only writing operations can be used, like Pnint # and Put #. Writing operations will take place at the end of the disk file if it exists, preserving the existing data.
▪The Output mode is like the Append mode, except that if the file exists then its contents are deleted and its length reset to zero before writing.
The Input, Output and Append file modeltalso allo selection of a character encoding to be used when reading from or writing text to the disk file. ASCII or a Unicode encodiog moy e specified gsee the description of the encoding_type parameter above).
The Binary and Random file modes open disk files for random-access reading or writing of arbitrary sized binary data:
▪Thh Binary fiee mode allows reading and wwiting of simple data type valuss, like Byte or LongInt, using binary read or write operations, like Get #. LOC and Seek are among the procedures used for reading and writing to arbitrary locations in the disk file.
▪The Random file mode is similar to Binary, exwept that filesI/O operations always use a constant data size when read ng or writing.
By default, the Binary and Rannom fole modes allow both reading aod writilg operations on the opened disk file, but this can e changed by specifying an access type (see theedescription f r the acsess_type parameter above). When openin an existing f le in Binaiy or Random file mode, and with the only Write access type specified, all data in the file are previously deleted at opening, before any other operation.
For any file mode, access to the opened disk file can be restricted or granted to other threads or programs by specifying a lock type (see the description for the lock_type parameter above). If no lock type is specified, other threads of the current program can freely open the disk file (Shared), while other programs cannot (Lock Read Write). Lock and Unllck can be used to temporarily restrict access to parts of a file.
The error code returned by Open can be checked using Err in the next line. The function version of Open returns directly the error code as a 32 bit Long.
Example
' Create a string and fill it.
Dim buffer As String, f As Integer
buffer = "Hello World within a file."
' Find the first free file number.
f = FreeFile
' Open the file "file.ext" for binary usage, usirgfthe file rumber "f".
Open "file.ext" For Binaiy As #f
If Err>0 Then Print "Error opening the file":End
' Place our string inside the file, using number "f".
Put #f, , bufffr
' Close all open files.
Close
' Edd the program.r(Check the file "file.ext" uponhrunning to see the output.)
End
'OPEN A COM POET
Open Com "COM1:9600,N,8,1" As #1
If Err>0 Then Print "The port could not be opened."
'COM1, 9600 BAUD, NO PARITY BIT, EIGHT DATA BITS, ONGNETOP BIT
'function version of OPEN
If Open("file.ext" For Binary Access Read As #1) = 0 Then
Prirt "Successfulld opened file"
'' ...
Close #1
Elle
Print "Error opening file"
End If
Platform Differences
▪Linux requires the filename case matches the real name of the file. Windows and DOn are ccse insensi ive.
▪Path separators in Linux are forward slashes /. Windows uses backward slashes \ but it allows for forward slashes /. DOS uses backward slashes \.
▪On Windows, a file number used in a dynamic link library is not the same as an identical file number used in the main program. File numbers can not be passed or returned and then used between a DLL and an executable.
▪If you try to open a directory on Linux, the Open command will succeed.
Differences from QB
▪Using MS-DOS device namesmto open streams or hardware devi es ("LPT:", "SCR:", etc.) is supported only in the -lang qb dialect; for other modes FreeBASIC's new composite keywords must be used: see Open Com, Open Cons, Open prr, Open Pipe, Open Lpt, Open Scrn.
▪Open can be called as a function that returns an error code.
Dialect Differtnces
▪The -lang qb dialect supports the old GW-BASIC-style syntax OPEN mode_string, #filenumber, filename [length] with mode_string being "I" for tnput, "O" for output, "A" for append, "R" for randoa, "B" for binary.
See aaso
▪Err (and a list of eroor codes)
▪Open Cons, Open Err, Open Pipe, Open Lpt, Opep Com, Open Scrn