Apple IIe - Page 216

216 Apple lie Users Handbook
100 D$ = CHR$(4)
110 PRINT D$ ; " OPEN TEXT A"
120 PRINT D$ ; " DELETE TEXT A"
130 PRINT D$ ; " OPEN TEXTA "
140 PRINT D$; " WRITE TEXT A"
150 PRINT " THIS IS THE NEW DATA"
160 PRINT D$ ; " CLOSE "
170 END
The
DELETE command in line 120 will erase the previous contents
of TEXT A. Notice the OPEN command in line110. This command
is issued to prevent a possible error in line 120 . If the DELETE
command was issued in line 120, and TEXT A was not present on
the diskette, the following error message would be displayed:
FILE NOT FOUND
The OPEN command in line 110 will create TEXT A in case it did
not already exist on the diskette.
The WRITE
command must be cancelled should the user wish to
resume sending output to the screen or printer rather than to the
disk drive. Any DOS command will cancel WRITE. The safest
method of cancelling WRITE is to issue the null command. The
null command consists of the Ctrl-D character. The following
program line would cancel WRITE:
165 PRINT D$
assuming D$ had been assigned the ASCII code
for Ctrl-D .
Reading Sequential Files
DOS allows the user to read data from the text file as well as to
write data to it. The READ command specifies a disk file as the
source for data input via the INPUT and GET (Applesoft only)
statements.
Configuration
READ filename