This function checks to see if the given file (passed as a string) exists and then checks upon its status (whether it can be opened etc). If necessary a standard error number is returned, otherwise ETAT will return 0, which means that the file can be accessed without the danger of an error such as “not found”. This can therefore be used to avoid the need for error trapping.
This program copies text files to window #1:
100 REPeat input_loop 110 INPUT "File to view:"!file$ 120 AnError=ETAT(file$) 130 IF NOT AnError: EXIT input_loop 140 PRINT "Sorry, ";: REPORT#1,AnError 150 END REPeat input_loop 160 OPEN_IN#3,file$ 170 REPeat view_file 180 IF EOF(#3) THEN EXIT view_file 190 INPUT#3,line$: PRINT line$ 200 END REPeat view_file 210 CLOSE#3
FTEST works like ETAT but recognises the default device and directory. FILE_OPEN, FOPEN, FOP_IN, FOP_OVER and FOP_NEW are all functions to open files without the need for error trapping. OPEN, OPEN_IN and OPEN_NEW stop with error messages if an error occurs. To avoid this, error trapping facilities, such as WHEN ERRor have to be used.