dopen - open RMSfile
DFILE *dopen (filename, mode)
Dopen opens the RMSfile named filename for future I/O. Dopen returns a pointer to a control block to identify the RMSfile in subsequent operations.
Filename is the pathname of the RMSfile to open.
Mode is a character string that states the types of operations to be done on the RMSfile. Mode may have one of the following values:
"r" open for reading
"w" zero RMSfile records, open for writing
"a" open for writing
"u" open for both reading and writing
RMS Programming Guide
Dopen returns the pointer NULL if filename cannot be accessed.