enabled.i4.v = fm_is_writing_enabled([vun.i2.r])

	This routine allows the program to determine if file writing
	is enabled at the FM level.  If "vun" is specified, only the
	status of that connection will be returned.

	[vun]		virtual unit number on which the file was opened
			(default is NULL - check overall status)

	This function returns status values as follows:

	CBS_NOTOPN		this VUN is not in use
	TRUE			writing enabled
	FALSE			writing disabled

	This function requires the following include files:

	cnsparam_h, cbslib_h, acnet_errors_h

	Related functions:

	fm_write_enable, fm_write_disable

	C/C++ usage:

	short	vun;
	int	enabled;

	enabled = fm_is_writing_enabled(&vun);