; Open the HDF file:  
filename = 'FID.hdf'  
hid = HDF_OPEN(filename,/CREATE)  
; Write two file annotations:  
HDF_DFAN_ADDFID, filename, 'File Annotation #1'  
HDF_DFAN_ADDFID, filename, 'File Annotation #2'  
; Read the two annotations back:  
HDF_DFAN_GETFID, filename, fid1  
HDF_DFAN_GETFID, filename, fid2  
HELP, fid1, fid2  
; Try to read a non-existent FID:  
HDF_DFAN_GETFID, filename, fid3  
; Read the FIRST fid again, using the FIRST keyword:  
HDF_DFAN_GETFID, filename, fid4, /FIRST  
HELP, fid4  
; Close the HDF file:  
HDF_CLOSE, hid  

IDL Output

FID1            STRING    = 'File Annotation #1'  
FID2            STRING    = 'File Annotation #2'  
  
% HDF_DFAN_GETFID: Could not read ID length  
  
FID4            STRING    = 'File Annotation #1'