System Functions
FFN( ) Find File Number
   
Format FFN(filename$ [ FROM fileno ] [ FOR OBJECT | EXCEPT OBJECT ] [ ,ERR=stmtref ] )

Where:

filename$ Name of the file to locate. String expression.
fileno Lowest channel number to start checking
stmtref Program line number or statement label to which to transfer control.
   
Returns Integer, channel/file number for open file or -1, if not open or accessible. In all cases, only files currently accessible will be returned.
   
Description This function checks all open files for any reference to the filename$ specified. The function returns the file number as an integer, if the file is open. If the file is not currently open on any channel, FFN( ) returns a value of -1.

The filename specified in FFN( ) must match the name used to OPEN the file; e.g.,

open(1)"cstfile
print ffn("/pvx/nomads/cstfile") ! Incorrect
-1
print ffn("cstfile") ! Correct
1

If a FROM fileno option is specified, the search starts with the file number provided.

By default, files that are open but reserved for use by an Object will not be checked unless the FFN function is executed within the object that has the file reserved.

The FOR OBJECT or EXCEPT OBJECT clauses can be used within an object to alter this behaviour. The FOR OBJECT will only return files numbers that are reserved for the current object whereas the EXCEPT OBJECT will return files that are generally accessible (i.e. not reserved exclusively by the current object). Use of the FOR/EXCEPT OBJECT clause when not in an object will generate an "Error #95: Bad Object Identifier"
   
Examples Read a record from the CUSTDBfile. If the file is not open, then open it on a Global file number.

0100 LET X=FFN("CUSTDB")
0110 IF X=-1 THEN LET X=GFN; OPEN (X)"CUSTDB"
0120 READ (X,KEY=CST_ID$,ERR=9000)IOL=%CST_IOL$

FFN( ) is case-sensitive (as is necessary in UNIX). To perform a case-insensitive search for the filename, set either 'FL' (lower case) or 'FU' (upper case) parameters.

0100 OPEN (5)"CSTfile" ! With neither 'FL' nor 'FU' set
-:PRINT FFN("CSTFILE")
-1
-:SET_PARAM 'FL'
-:PRINT FFN("CSTFILE")
5
-:PRINT FFN("cstFILE")
5

Forward slashes may be used in place of backslashes.

open(1)"\pvx\nomads\cstfile"
print ffn("/pvx/nomads/cstfile")
1

A leading ./ or .\ is ignored by the FFN( ) function.

open(1)"./cstfile print ffn("cstfile")
1