Open a file.
The function will return 0 if the file has been opened successfully in which case the File variable is initialised and can then be used in the remaining file operations.
A negative return value indicates an error as follows:-
-1 = The file doesn't exist when opening for read
-2 = The file already exists when opening for write
-3 = The directory doesn't exist
-4 = You are trying to write a read only file
-5 = The disk is full
-6 = The mode parameter is invalid
variable to store the details on the open file.
The filename in DOS format.
ie the filename can be 8 characters, a full stop, followed by a 3 character extension.
Indicates how you want to use the file:
'r' - To open an existing file for read access
'w' - To create a new file for read write access
'a' - To write to the end of an existing file (ie append), or create the file if it doesn't exist.