FOPEN
FOP_DIR
FOP_IN
FOP_NEW
FOP_OVER

Syntax: FOPEN (#ch, name)  or   FOPEN (name)
   and: FOP_DIR (#ch, name)  or   FOP_DIR (name)
   and: FOP_IN (#ch, name)  or   FOP_IN (name)
   and: FOP_NEW (#ch, name)  or   FOP_NEW (name)
   and: FOP_OVER (#ch, name)  or   FOP_OVER (name)
Location: Toolkit II, THOR XVI

These function are intended to let you open files and trap errors.

They are very similar to other commands:

FOPEN -------- OPEN
FOP_DIR ------ OPEN_DIR
FOP_IN ------- OPEN_IN
FOP_NEW ------ OPEN_NEW
FOP_OVER ----- OPEN_OVER


If the specified channel is successfully opened, then the functions return 0.

If the second variant of these functions is used, if successful, FOPEN will return a positive number representing the number of the next available channel.

Examples:
ERRno=FOPEN(#3,scr_448x200a32x16)   
Chan=FOPEN('flp1_Input_dat'): IF Chan>0 THEN INPUT #Chan,x

CROSS-REFERENCE:
ERNUM contains details of the various error messages. 
WHEN ERRor allows you to error trap a complete program. 
FTEST allows you to test the status of a file without (explicitly) opening a channel.
