;---------------------------------------------------------------------------
; Document name: UTC2DIFF.PRO
; Created by:    Dietmar Germerott, MPAE Lindau, July 7, 1999
;
; Last Modified: Wed Jul  7 13:42:01 1999 (GERMEROTT@linsu1.mpae.gwdg.de)
;---------------------------------------------------------------------------
;
FUNCTION utc2diff, intime, start_time=start_time, errmsg=errmsg
;+
; PROJECT:
;       SOHO - SUMER
;
; NAME:
;       UTC2DIFF()
;
; PURPOSE: 
;       Compute the difference in days between two dates
;
; CATEGORY:
;       Time calculation
; 
; EXPLANATION:
;       UTC2DIFF calculates the difference in days between
;       the start date (start_time) and end date (intime).
;       The Keyword START_TIME is optional to give another
;       start date as the default. The default start date
;       is 2-dec-1995 which is day 1.
;       If intime is equal start_time it result as day 1
;   
; SYNTAX: 
;       Result = utc2diff()
;
; EXAMPLES:
;       
; INPUTS:
;       intime - date to calculate the difference
;
; OPTIONAL INPUTS: 
;       None.
;
; OUTPUTS:
;       Difference in days between input dates
;
; OPTIONAL OUTPUTS:
;       None.
;
; KEYWORDS: 
;       start_time - start date for calculation
;              default start date is 2-dec-1995 (SOHO launch)
;
;
; COMMON:
;       None.
;
; RESTRICTIONS: 
;       None.
;
; SIDE EFFECTS:
;       None.
;
; HISTORY:
;       Version 1, July 7, 1999, Dietmar Germerott, MPAE Lindau. Written
;
; CONTACT:
;       Dietmar Germerott, MPAE Lindau (Dietmar Germerott@linmpi.mpg.de)
;-
;
   ON_ERROR, 2
   errmsg = ''
   
   IF N_PARAMS() LT 1 THEN BEGIN
      
      PRINT, 'UTC2DIFF -- Syntax error.'
      PRINT, '   Usage: Result=UTC2DIFF(intime [,start_time=xxx [,errmsg=errmsg]])'
      PRINT, ' '
      PRINT, ' Example:'
      PRINT, ' '
      PRINT, "   Result=UTC2DIFF('25-FEB-1999')"
      PRINT, '   This example returns the diffrence in days between'
      PRINT, '   2-dec-1995 (default) and 25-feb-1999'
      PRINT, ' ' 
      PRINT, "   Result=UTC2DIFF('25-FEB-1999',start='1-JAN-1999')"
      PRINT, '   This example returns the diffrence in days between'
      PRINT, '   1-JAN-1999 and 25-feb-1999'
      PRINT, ' ' 
      RETURN,-1
   ENDIF
   
   IF KEYWORD_SET(start_time) THEN s_date = start_time ELSE $
      s_date = '02-DEC-1995'
   
   s_datemjd = anytim2utc(s_date,errmsg=errmsg)
   IF errmsg NE '' THEN GOTO, handle_error
   
   e_datemjd = anytim2utc(intime,errmsg=errmsg)
   IF errmsg NE '' THEN GOTO, handle_error
   
   diff_day = e_datemjd.mjd + 1 - s_datemjd.mjd
   
   RETURN, diff_day
handle_error:
   MESSAGE, /cont, errmsg
   RETURN,-1
END


;---------------------------------------------------------------------------
; End of 'UTC2DIFF.PRO'.
;---------------------------------------------------------------------------