Return a structure as defined in the names and values data.
struct = MRD_STRUCT(NAMES, VALUES, NROW, STRUCTYP='name' )
NAMES = A string array of names of structure fields.
VALUES = A string array giving the values of the structure
fields. See examples below.
NROW = The number of elements in the structure array.
A structure as described in the parameters or 0 if an error
OPTIONAL KEYWORD PARAMETERS:
/NO_EXECUTE - If set then the use of the EXECUTE() statement is avoided.
By default, the NO_EXECUTE pathway is used if IDL is
running under the Virtual Machine. Note if /NO_EXECUTE
is set, then the user cannot supply arbitary values, but
all possible values used by MRDFITS will be allowed.
STRUCTYP = The structure type. Since IDL does not allow the
redefinition of a named structure it is an error
to call MRD_STRUCT with different parameters but
the same STRUCTYP in the same session. If this
keyword is not set an anonymous structure is created.
May create a temporary file if the structure definition is too long
for the EXECUTE function and using old style structures
By default, the program defines the structure in a long string
which is executed with CREATE_STRUCT within a single EXECUTE statement.
If program is being run in the IDL Virtual machine (EXECUTE statement
not allowed), then a separate CREATE_STRUCT statement is called
for each tag. This mode does not have the full capabilities of the
normal mode, but should be sufficient for use with MRDFITS().
A structure definition is created using the parameter values.
MRD_NSTRUCT is called and generates the structure in pieces using the
execute and create_struct keywords.
(1) str = mrd_struct(['fld1', 'fld2'], ['0','dblarr(10,10)'],3)
Note that "0" is always considered short integer even if the default
integer is set to long.
(2) str = mrd_struct(['a','b','c','d'],['1', '1.', '1.d0', "'1'"],1)
; returns a structure with integer, float, double and string
GETTOK() - needed for virtual machine mode only
Created by T. McGlynn October, 1994.
Modified by T. McGlynn September, 1995.
Added capability to create substructures so that structure
may contain up to 4096 distinct elements. [This can be
increased by futher iteration of the process used if needed.]
Removed V4.0 reference to common block October 1997
Allowed unlimited number of structure elements if the version
is greater than 5.0. Put back in code to handle prior versions.
The  will need to be translated back to () for this to
work. T. McGlynn December 15 1998.
Add MRD_NSTRUCT since IDL has mysterious problems compiling
very large structures.
Removed TEMPDIR and OLD_STRUCT keywords W. Landsman October 2003
Alternate pathway without EXECUTE for V6.0 virtual machine, D. Lindler
Removed limit on EXECUTE statement. W. Landsman October 2003
Restore EXECUTE limit (sigh...), added NO_EXECUTE keyword
W. Landsman July 2004
Fix use of STRUCTYP with /NO_EXECUTE W. Landsman June 2005
Assume since V6.0 (lmgr function available), remove 131 string length
limit for execute W. Landsman Jun 2009
Restore EXECUTE limit (sigh...) W. Landsman July 2009
Make sure "0" is a short integer even with compile_opt idl2 July 2010
Added "0.0", "0.0d", "0u", "0ul", and "0ull" as valid tags
for /NO_EXECUTE E. Rykoff May 2012