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Re: [Chicken-users] do I use define-foreign-variable correctly ?
From: |
Kon Lovett |
Subject: |
Re: [Chicken-users] do I use define-foreign-variable correctly ? |
Date: |
Wed, 7 Feb 2007 10:31:12 -0800 |
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On Feb 7, 2007, at 6:41 AM, minh thu wrote:
#>!
#include <X.h>
#include <keysym.h>
<#
(define-foreign-variable c-escape-key int "XK_Escape")
(define escape-key c-escape-key)
Do I need to have those two lines too be able to use escape-key as a
Scheme symbol for the C #defined XK_Escape value ?
Umm, depends. Do you want it visible outside of the compilation unit
(i.e. exportable)? then '(define escape-key (foreign-value
"XK_Escape" int))' is enough. (I might make the symbol uppercase just
to emphasize it is a constant.) Also 'define-foreign-variable' has
overhead that you don't want for a constant, it isn't mutable so
conversion should only be done once. ('foreign-value' is a wrapper
around 'define-foreign-variable' that creates the variable, gets its'
value, & throws away the variable, returning only the value.)
Thanks,
thu
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