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open   statement



Syntax:
open "method[fork]",fileID,ref,recLen

Description:
This statement opens a file so that you can read from it and/or write to it. If you specify a method other than "I", the open statement also creates the file if it doesn't already exist.
The parameters are interpreted as follows:

 method
Specify one of the following letters:

IOpen for input (reading) only. The file must already exist. Other processes may read from the file (but not write to it) while it's open with this method.
OOpen for output (writing) only. If the file already exists, all of its current contents will be destroyed. You have exclusive access to the file (no other process can read from it nor write to it) while it's open with the "O" method. Does NOT support the "resource fork" open.
ROpen for "random access." You can either read from or write to the file. The "file mark" (which indicates where the next read or write operation will occur) is placed initially at the beginning of the file. If you write to the file, you only replace those bytes which you're writing; the rest of the file's contents are unaffected. You have exclusive access to the file.
AOpen for "append." This is just like method "R", except the file mark is placed initially at the end of the file. This method is normally used when you want to add data to the end of an existing file.
NOpen for non-exclusive random access. This is just like method "R", except that other processes may read from the file while you have it open. Your process is the only one allowed to write to the file and your code is responsible for assuring file readers don't process old or partial data. OPEN code only provides access; it does not provide any data integrity protection when there are concurrent readers and writers of the same file. If a file is already open in "N" mode, a second attempt to open in 'N' mode by the current or other process automatically provides read-only access ( essentially "I" mode ) to the file. If the process is given read-only mode, the FB runtime sends a "file already open with write permission" ( _opWrErr ) error code which can used by the caller ( must be trapped with 'on error' and "error" )

 fork
Resource forks are no longer supported and Apple has long recommended other approaches. Data fork is supported by default and does not require a fork specification.

DOpen the "data fork." Data fork is supported by default and does not need to be specified.
ROpen the "resource fork." Obsolete and not supported as of FB version 5.7.99.

 fileID
Specify a number in the range 1 through 255 which is not being used by any other currently open file. You can use this number to identify the open file in statements and functions such as read#, write, eof, lof, etc. The fileID number is associated with the file until you close the file.

 ref
The 'ref' must be a CFURLRef. Appendix A - File Object Specifiers, describes the composition of a 'CFURLRef' type. Open syntax xamples are:
open "I", 1, @urlA CFURL object is used
open "I", 1, @urlA CFURL object is used
open "O", 3, @url A CFURL object is used
open "I", 2, @url A CFURL object is used.
open "A", 5, @url A CFURL object is used.
open "R", 2, @url A CFURL object is used.
open "I", 2, @url A CFURL object is used.

 recLen
This value indicates the length of the records in the file; naturally, it's most useful when the file consists of fixed-length records. The value you specify is used when you execute statement and functions such as record, rec, loc and lof. If you omit this parameter, a default value of 256 is used. If the file doesn't consist of fixed-length records, it's often most convenient to set recLen to 1.

See Also:
close; inkey$; input#; print#; read#; read file; read field; write; write file; write field; record; rec; loc; lof; eof; files$