On Jun 17, 12:25 am, Jeremy Bailin <astroco...@gmail.com> wrote:
> I'm sure there is a simple answer to this, but I can't find it.
>
> Does someone know of a programmatic way to determine if a given tag is
> defined in a structure, without resorting to TAG_NAMES (which seems
> downright ugly). I can do something like
>
> if n_elements(variable) eq 0
>
> to determine if a variable has been defined, but to figure out if a
> structure tag is defined I need to grab a list of all tags?? I guess I
> want something that's functionally equivalent to:
>
> if total(tag_names(struct) eq strupcase(tag)) gt 0
>
> but which doesn't make me shudder. The closest discussion I can find
> on this is here:http://groups.google.com/group/comp.lang.idl-pvwave/bro wse_thread/thr...
> ...but most of that focuses on the peculiarities of dealing with
> _EXTRA, not the more generic case.
>
> -Jeremy.
I wrote a function a few years ago that can be used on deep / complex
structures to tell if a tag exists. It uses tag_names, but since it is
encapsulated maybe it is more palatable to you. Uses recursion to
check nested structures.
;
;+
; NAME:
; XIASTREC
;
; PURPOSE:
; XIASTREC Is A Structure Tag Recursive Existence Checker
;
; CATEGORY:
; Structures, utility, recursion
;
; CALLING SEQUENCE:
; result = XIASTREC( struct, tag_list )
;
; INPUTS:
; Struct: A structure
;
; OPTIONAL INPUTS:
; tag_list: A string array that contains the tags, subtags,
; subsubtags, etc. whose existence you wish to verify
;
; KEYWORD PARAMETERS:
; DEBUG: Print some debug info
;
; OUTPUTS:
; This function returns 1 if the struct, or struct.tag, or
; struct.tag.tag.tag... exists, and 0 if it does not. It returns -1
; if called incorrectly.
;
; PROCEDURE:
; 1. Check if the struct is valid
; 2. Check if tags were passed in. If so, does tag[0] exist in
struct?
; 3. Recurse, checking if tag[1] exist in the struct that is tag[0].
;
; EXAMPLE:
; PRINT, XIASTREC( foo ) ; 0, foo not defined
; PRINT, XIASTREC( !P, 'thick' ) ; 1, !P.THICK exists
;
; x = { foo:{bar:42}, baz:'Goodbye Cruel World' }
; PRINT, XIASTREC( x, 'bar' ) ; 1, x.bar exists
; PRINT, XIASTREC( x, ['foo', 'baz'] ) ; 0, x.foo.baz does not exist
; PRINT, XIASTREC( x, ['foo', 'bar' ] ) ; 1, x.foo.bar exists
; PRINT, XIASTREC( x, ['foo', 'bar', '42' ] ) ; 0, bar=42, not bar.
42
;
; MODIFICATION HISTORY:
; Written by: KDM, 2007-07-15
;
;-
function XIASTREC, s, tags_t, debug=debug,
recursive_level=recursive_level
if keyword_set(debug) then dbg = 1 else dbg = 0
if size(s,/type) ne 8 then begin
if dbg then MESSAGE, "Struct is not of type STRUCT", /CONTINUE
return, 0
endif
;; only S passed in. It is a struct. We're done.
if n_params() eq 1 then begin
if dbg then MESSAGE, "Struct is existent struct", /CONTINUE
return, 1
endif
tags = STRUPCASE(tags_t)
;; if here, two params passed in
if size( tags, /type ) ne 7 then begin
MESSAGE, "ERR: Tags must be of type STRING", /CONTINUE
return, -1
endif
names = tag_names( s )
idx = where( names eq tags[0], count )
if count eq 0 then begin
if dbg then MESSAGE, "Tag '"+tags[0]+"' not in struct", /CONTINUE
return, 0
endif
;; only 1 tag, and it matched
if n_elements(tags) eq 1 then begin
if dbg then MESSAGE, "Tag '"+tags[0]+"' found", /CONTINUE
return, 1
endif
if keyword_set(recursive_level) then r = recursive_level else r = 0
if dbg then begin
if r eq 0 then MESSAGE, "Beginning recurse...", /CONTINUE
spaces = ''
for i=0,r-1 do spaces=spaces+' '
MESSAGE, spaces + "Recursing to level " + STRTRIM(r,2), /CONTINUE
endif
;; recurse! :)
exists = XIASTREC( s.(idx), tags[1:*], $
debug=debug, recursive_level=r+1 )
if dbg then MESSAGE, spaces+"Level "+STRTRIM(r,2)+" completed", /
CONTINUE
return, exists
MESSAGE, "ERR: Shouldn't be here...", /CONTINUE
return, -1
end
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