| Re: Global Variable [message #26836 is a reply to message #19399] |
Mon, 01 October 2001 02:40  |
Martin Downing
Messages: 136
Registered: September 1998
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Senior Member |
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First comment is to only use global variables sparingly, sometimes they are
appropriate but try not to rely on them to make programming simpler.
I know of three ways, the SYSTEM variables are fully global, and may be user
defined, COMMON BLOCK variables are shared between those routines which
include a
declaration for the common block, these are very suitable for those programs
where you cant find a way of writing your code without creating global
variables, but do not want the variables to be seen by any old routine.
system variable eg:
------------
IDL>filepaths = {tag:"FILEPATHS", bin:bin)
IDL>defsysv, '!fpaths',filepaths ; a variable for local paths
now you can use this variable from anywhere in your code as:
IDL> print, !fpaths.bin
d:\martin\bin\
------------
For common block variables you need a block identifier then a list of
variables in the block. Note that the order is all that is relevent and that
the first declaration defines the size of the block: eg
pro foo
COMMON FOO_COMMON_VARIABLES, a,b,c,d
a = "first"
b="second"
c="third"
d="fourth"
print_foo
end
pro print_foo
; note later calls do not have to decare all block variables
COMMON FOO_COMMON_VARIABLES, d,c,var3
print, d
print, c,
print, var3
end
the result of calling this procedure is demonstrates that there is no
association between variable names inthe common block just the variable
order.
IDL> foo
first
second
third
------------------------------
Lastly there is a *really* nice way of passing around all the 'global'
variables you need in your widget programs using get/set_uvalue which. This
is my favourite tip learnt from David's books so I shall leave him to
describe. In essence you call:
WIDGET_CONTROL, base, SET_UVALUE=info_structure
WIDGET_CONTROL, event.top, GET_UVALUE=info_structure
cheers
Martin
----------------------------------------
Martin Downing,
Clinical Research Physicist,
Orthopaedic RSA Research Centre,
Woodend Hospital, Aberdeen, AB15 6LS.
"Miguel �ngel C�rdoba" <cordoba@ehma.upc.es> wrote in message
news:3BB82DB7.265E2670@ehma.upc.es...
> Anybody know how can I define al global variable?.
>
> Thanx.
>
> --
> +- - - - - - - - - - - - - - - - - - - - - - - -+
> | Miguel Angel C�rdoba cordoba@ehma.upc.es |
> | |
> | http://campus.uab.es/~2034008 |
> | |
> | Grup de Modelitzaci� Hidrometeorol�gica (UPC) |
> | (http://www.upc.es/ehma/gmh) |
> +- - - - - - - - - - - - - - - - - - - - - - - -+
>
>
>
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