How to get numbers into passed structure elements (pass-by-value/reference

Hello,

This subject comes around every now and again, but I can't find anything
useful searching.

I'm calling a function, CRTM_Read_Atmosphere_Record(), like so:


   Atm = PTRARR(n_Profiles)
   FOR m = 0, n_Profiles-1 DO BEGIN
     Atm[m] = PTR_NEW({CRTM_Atmosphere})
     result = CRTM_Read_Atmosphere_Record( FileID, *Atm[m], DEBUG=Debug )
     ...check result....
   ENDFOR


That function in turns calls another function, CRTM_Read_Cloud_Record(),
like so:


FUNCTION CRTM_Read_Atmosphere_Record, FileID     , $  ; Input
                                       Atm        , $  ; Output
                                       DEBUG=Debug     ; Optional input
   .....
   FOR n = 0, Atm.n_Clouds-1 DO BEGIN
     result = CRTM_Read_Cloud_Record( FileID, (*Atm.Cloud)[n], DEBUG=Debug
)
     ...check result....
   ENDFOR


And inside the CRTM_Read_Cloud_Record() function I do the following:


FUNCTION CRTM_Read_Cloud_Record, FileID           , $  ; Input
                                  Cloud            , $  ; Output
                                  DEBUG=Debug           ; Optional input
   .....
   Type = Cloud.Type
   READU, FileID, Type, $
                  *Cloud.Effective_Radius, $
                  *Cloud.Effective_Variance, $
                  *Cloud.Water_Content
   Cloud.Type = Type

(and similar for an Aerosol structure and I/O function. Also, assume the
pointer component 
allocation has been done to the correct array size))

As you have probably guessed, by the time I inspect all the data that is
returned in the 
original Atm pointer array, everything is fine *except* the cloud type
flag. It is zero.

So, I realise this is one of those pass-by-reference or pass-by-value
things, but how does 
one get around it? Do I:
   a) make the Type component of the Cloud structure a pointer? (Yuk!)
   b) change the way I pass the Cloud structure into the
CRTM_Read_Cloud_Record() fn?
      i.e. not reference the cloud structure array via the index [n].

I would much prefer (b), but will that entail copying entire structures?
The number of 
"Clouds" associated with any particular "Atm[m]" profile is variable.

Thanks for any info.

cheers,

paulv


p.s. FWIW, the structure definitions are:

PRO CRTM_Atmosphere__Define
   void = { CRTM_Atmosphere, $
            n_Layers       : 0L, $
            n_Absorbers    : 0L, $
            n_Clouds       : 0L, $
            n_Aerosols     : 0L, $
            Climatology    : 0L, $
            Absorber_ID    : PTR_NEW(), $
            Absorber_Units : PTR_NEW(), $
            Level_Pressure : PTR_NEW(), $
            Pressure       : PTR_NEW(), $
            Temperature    : PTR_NEW(), $
            Absorber       : PTR_NEW(), $
            Cloud          : PTR_NEW(), $
            Aerosol        : PTR_NEW()  }
END

and

PRO CRTM_Cloud__Define
   void = { CRTM_Cloud, $
            n_Layers           : 0L, $
            Type               : 0L, $
            Effective_Radius   : PTR_NEW(), $
            Effective_Variance : PTR_NEW(), $
            Water_Content      : PTR_NEW()  }
END