FUNCTION FXBDIMEN, UNIT, COL, ERRMSG=ERRMSG
;+
; NAME:
;     FXBDIMEN()
;
; Purpose     :	Returns the dimensions for a column in a FITS binary table.
;
; Explanation :	This procedure returns the dimensions associated with a column
;		in a binary table opened for read with the command FXBOPEN.
;
; Use         :	Result = FXBDIMEN(UNIT,COL)
;
; Inputs      :	UNIT	= Logical unit number returned by FXBOPEN routine.
;			  Must be a scalar integer.
;
;		COL	= Column in the binary table to read data from, either
;			  as a character string containing a column label
;			  (TTYPE), or as a numerical column index starting from
;			  column one.
;
; Opt. Inputs :	None.
;
; Outputs     :	The result of the function is an array containing the
;		dimensions for the specified column in the FITS binary table
;		that UNIT points to.
;
; Opt. Outputs:	None.
;
; Keywords :	ERRMSG	= If defined and passed, then any error messages will
;			  be returned to the user in this parameter rather than
;			  depending on the MESSAGE routine in IDL.  If no
;			  errors are encountered, then a null string is
;			  returned.  In order to use this feature, ERRMSG must
;			  be defined first, e.g.
;
;				ERRMSG = ''
;				Result = FXBDIMEN( ERRMSG=ERRMSG, ... )
;				IF ERRMSG NE '' THEN ...
;
; Calls       :	FXBCOLNUM, FXBFINDLUN
;
; Common      :	Uses common block FXBINTABLE--see "fxbintable.pro" for more
;		information.
;
; Restrictions:	None.
;
; Side effects:	The dimensions will be returned whether or not the table is
;		still open or not.
;
;		If UNIT does not point to a binary table, then 0 is returned.
;
;		If UNIT is an undefined variable, then 0 is returned.
;
; Category    :	Data Handling, I/O, FITS, Generic.
;
; Prev. Hist. :	None.
;
; Written     :	William Thompson, GSFC, 4 March 1994.
;
; Modified    :	Version 1, William Thompson, GSFC, 4 March 1994.
;		Version 2, William Thompson, GSFC, 21 June 1994
;			Added ERRMSG keyword.
;		Version 3, William Thompson, GSFC, 23 June 1994
;               	Modified so that ERRMSG is not touched if not defined.
;
; Version     :	Version 3, 23 June 1994
;	Converted to IDL V5.0   W. Landsman   September 1997
;-
;
@fxbintable
	ON_ERROR, 2
;
;  Check the number of parameters.
;
	IF N_PARAMS() NE 2 THEN BEGIN
		MESSAGE = 'Syntax:  Result = FXBDIMEN(UNIT,COL)'
		IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN
			ERRMSG = MESSAGE
			RETURN, 0
		END ELSE MESSAGE, MESSAGE
	ENDIF
;
;  If UNIT is undefined, then return zero.
;
	IF N_ELEMENTS(UNIT) EQ 0 THEN RETURN, 0
;
;  Check the validity of UNIT.
;
	IF N_ELEMENTS(UNIT) GT 1 THEN BEGIN
		MESSAGE = 'UNIT must be a scalar'
		IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN
			ERRMSG = MESSAGE
			RETURN, 0
		END ELSE MESSAGE, MESSAGE
	ENDIF
	SZ = SIZE(UNIT)
	IF SZ[SZ[0]+1] GT 3 THEN BEGIN
		MESSAGE = 'UNIT must be an integer'
		IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN
			ERRMSG = MESSAGE
			RETURN, 0
		END ELSE MESSAGE, MESSAGE
	ENDIF
;
;  Find the column number for the requested column.
;
	IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN
		ICOL = FXBCOLNUM(UNIT,COL,ERRMSG=ERRMSG)
		IF MESSAGE NE '' THEN RETURN, 0
	END ELSE ICOL = FXBCOLNUM(UNIT,COL)
	IF ICOL EQ 0 THEN BEGIN
		MESSAGE = 'No such column'
		IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN
			ERRMSG = MESSAGE
			RETURN, 0
		END ELSE MESSAGE, MESSAGE
	ENDIF
;
;  Get the dimensions associated with UNIT and COL.
;
	ILUN = FXBFINDLUN(UNIT)
	DIMS = N_DIMS[*,ICOL-1,ILUN]
	IF N_ELEMENTS(ERRMSG) NE 0 THEN ERRMSG = ''
	RETURN, DIMS[1:DIMS[0]]
;
	END