HDF_DF24_LASTREF

; Open an HDF file. 
h=HDF_OPEN('myhdf.hdf')  
PRINT, HDF_DF24_LASTREF()  
; IDL prints 0, meaning that the call was successful,  
; but no reference number was available. 
 
; Create a 3D array, representing a 24-bit image: 
a = BINDGEN(3,100,100)    
 
; Write the 24-bit image to the file: 
HDF_DF24_ADDIMAGE, 'myhdf.hdf', a 
 
PRINT, HDF_DF24_LASTREF() 
; IDL prints a reference number for the last operation  
; (for example, 2). Note the reference number is not  
; simply a 1-based "image number"; the reference number  
; could easily be "2" or "3", etc. 
 
; Write another image to the file: 
HDF_DF24_ADDIMAGE, 'myhdf.hdf', a    
 
; Print the last reference number: 
PRINT, HDF_DF24_LASTREF() 
PRINT, HDF_DF24_NIMAGES('myhdf.hdf') 
; IDL prints "2" because we've written two images to the file. 
; Close the file 
HDF_CLOSE, h