The uopen command opens a given file name to a file variable.
UOPEN <path> [FOR {READWRITE|READ|WRITE}] TO FileHandle THEN statement(s)
ELSE statement(s)
| path | File expressed by the valid path name, within quotes. |
| FileHandle | Must be used for all future references to the file. |
The file pointer is positioned at the beginning of the file. The path points to a path naming a file. If an error occurs or the file does not exist, the ELSE clause executes.
One reason that the uopen command may fail is that the user attempting to open the file does not have the necessary permissions. For example, if the file contains confidential information that the user is not authorized to read, the uopen command does not open the file. The ELSE clause executes instead.
FileHandle is a variable that is returned from the uopen command and must be used for subsequent accesses to this file. The FileHandle variable is the file descriptor of the file on the host system. If the file cannot be opened, the ELSE clause executes.
FILEDES1 contains the file descriptor that allows the user to access the \books\chap4.txt file. In the following statement, the file is opened for READ only. Any attempt to write to the file using this file descriptor results in an error.
UOPEN “c:\books\chap4.txt” FOR READ TO FILEDES1 ELSE STOP
The following statement opens the chap4.txt file located in the current directory. FILEDES2 contains the file descriptor necessary to open the chap4.txt file. The file is opened for WRITE only. If the UREAD command is used, an error results. If the file cannot be opened for any reason, the message in the ELSE clause displays.
UOPEN “chap4.txt” FOR WRITE TO FILEDES2 ELSE PRINT “CAN NOT OPEN FILE!”
The next statement opens the chap4.txt file located in the parent directory of the current directory. If the file can be opened for reading and writing, FILEDES3 contains the file descriptor allowing access to the file. If an error occurs, the ELSE clause executes.
UOPEN “..\chap4.txt” FOR READWRITE TO FILEDES3 ELSE STOP
The last statement opens the chap4.txt file for reading and writing. After the file is opened, FILEDES4 contains the file descriptor that allows access to the chap4.txt file. If an error occurs, the ELSE clause executes.
UOPEN “chap4.txt” TO FILEDES4 ELSE STOP