• Use call_external
  
  
• supply the name of the dll
  
  
• supply the name of the routine in the dll
  
  
• call_external loads the routine from the dll and always passes two arguments:
  
  
  • argc - the number of arguments
    
    
  • argv - the addresses of the arguments
  
  
• both arguments are integers regardless of the data which they describe
  
  
• both arguments are required even if the argument count is zero
  
  
• this is tricky to deal with on receipt
  
  
• looks like the following:

   call_external( 'testsub',        $  ; IDL adds .dll on Windows
                  'sum_1d_array',   $  ; looks for the dll on PATH
                   n, array, total )