STR_DIFF will is a boolean function which returns true (1) when differences
are found between the two input structures. If no
differences are found, it returns false (0).
IDL> qdiff = str_diff(index1, index2)
IDL> qdiff = str_diff(index1, index2, /diff
IDL> qdiff = str_diff(index1, index2, dtnames=dtnames
where /diff will only check the tag names. 
is an
optional input list of the tag names which should be checked (the default is to check all tags).
You can get a list of the tags whose values differ by using the
optional keyword output, 
.
STR_DIFF is not recursive.