;+
;
; @file_comments
; Translate a structure in a string able to be used to specify keywords 
; in the calling of a function when we use EXECUTE (see example)
;
; @categories 
; 
; @param STRUCT
; a structure
;
; @returns
; a string composed like following:
; For each element of the structure, we write a part of the string as: 
;         'name_of_the_element=content_of_the_element'
;
; @restrictions
; If an element of the structure contain an array, it will be convert in a vector.
;
; @restrictions
; Beware, this function has loops, ifs ad cases everywhere. So it can 
; not be used by big keywords (with a lot of elements which are big 
; arrays). The input keyword must not contain Complex floatings, structure, 
; Double-precision complex, Pointer, Object reference, Unsigned Integer, 
; Unsigned Longword Integer, 64-bit Integer or Unsigned 64-bit Integer.
;
; @examples
; We create a structure
;       IDL> b=get_extra(ok=111, year=[1997,1998,1999], age_capitaine=35)
;       IDL> help, b,/struct
;       ** Structure <817f4bc>, 3 tags, length=10, refs=1:
;          AGE_CAPITAINE   INT             35
;          OK              INT            111
;          YEAR            INT       Array[3]
; We put this structure as a string
;       IDL> a=strkeywd(b)
;       IDL> print, a
;       AGE_CAPITAINE=35, OK=111, YEAR=[1997,1998,1999]
; Now we can use the string a to pass keywords in a function thanks to execute!!
;       IDL> test=execute('c=get_extra('+a+')')
;       IDL> help, c,/struct
;       ** Structure <817f2dc>, 3 tags, length=10, refs=1:
;          AGE_CAPITAINE   INT             35
;          OK              INT            111
;          YEAR            INT       Array[3]
;
; @history
; Sebastien Masson (smasson\@lodyc.jussieu.fr)
;                      11/10/1999
;
; @version
; $Id$
;
;-
FUNCTION strkeywd, struct
;
  compile_opt idl2, strictarrsubs
;
   if size(struct, /type) NE 8 then return,  ''
   tname = tag_names(struct)
   if n_elements(tname) EQ 0 then return,  ''
;------------------------------------------------------------
; on s''occupe du premier element
;------------------------------------------------------------
   res = strlowcase(tname[0])+'='+tostr(struct.(0))
   if n_elements(tname) EQ 1 then return,  res
;------------------------------------------------------------
; on s''occupe des autres elements
;------------------------------------------------------------
   for n = 1,n_elements(tname)-1 do res = res+', '+strlowcase(tname[n])+'='+tostr(struct.(n))
;
   return,  res
end