define-foreign-variable the-name &key type accessor language
no-check module => lisp-name
the-name ::= lisp-name | (lisp-name foreign-name [encoding ])
encoding
::= :source | :object | :lisp | :dbcs
accessor
::= :value | :address-of | :read-only | :constant
Names the Lisp function which is used to access the foreign variable.
A symbol naming the Lisp accessor.
A string or a symbol specifying the foreign name of the variable.
An option controlling how the Lisp variable name is translated to match the foreign variable name in the foreign DLL. The encoding option can be one of the following:
:source
tells LispWorks that
foreign-name
is the name of the variable in the foreign source code. This is the default value of
encoding
when
foreign-name
is a string.
:object
tells LispWorks that
foreign-name
is the literal name of the variable in the foreign object code.
:lisp
tells LispWorks that if
foreign-name
is a Lisp symbol, it must be translated and encoded. This is the default value of
encoding
if
foreign-name
is a symbol.
:dbcs
modifies the variable name on Windows, as described for define-foreign-function.
The FLI type corresponding to the type of the foreign variable to which Lisp is interfacing.
An option specifying what kind of accessor is generated for the variable. It can be one of the following:
:value
gets the value of the foreign variable directly. This is the default value when
type
is a non-aggregate type. (There is no default
accessor
for aggregate types.)
:address-of
returns a FLI pointer to the foreign variable.
:read-only
ensures that no
setf
method is defined for the variable, which means that its value can be read, but it cannot be set.
:constant
is like
:read-only
and will return a constant value. For example, this is more efficient for a variable that always points to the same string.
The language in which the foreign source code for the variable is written. The default is
:ansi-c
.
If
nil
, the types of the arguments provided when the Lisp function is called are compared with the expected types and an error is raised if they do not match. Setting
no-check
to
t
overrides this check.
A string or symbol naming the module in which the foreign variable is defined.
The macro
define-foreign-variable
defines a Lisp accessor which can be used to get and set the value of a variable defined in foreign code.
If the foreign variable has a type corresponding to an FLI aggregate type, then
accessor
must be supplied (there is no default). If
accessor
is
:value
, then a copy of the object is allocated using allocate-foreign-object, and the copy is returned. In general, it is more useful to use
accessor
:address-of
for aggregate types, to allow the original aggregate to be updated.
If you specify any of the FLI float types :float, :double, :lisp-float, :lisp-single-float and so on, then the value of
language
should be
:ansi-c
.
module is processsed as for define-foreign-function.
The following example illustrates how to use the FLI to define a foreign variable, given the following C variable in a DLL:
int num;
The first example defines a Lisp variable,
num1
, to interface with the C variable
num
.
(fli:define-foreign-variable (num1 "num") :type :int)
The following commands return the value of
num
, and increase its value by 1:
(num1)
(incf (num1))
In the next example, the Lisp variable
num2
interfaces with
num
in a read-only manner.
(fli:define-foreign-variable (num2 "num")
:type :int :accessor :READ-ONLY)
In this case, the next command still returns the value of
num
, but the second command raises an error, because
num2
is read-only.
(num2)
(incf (num2))
The final example defines a Lisp variable,
num3
, which accesses
num
through pointers.
(fli:define-foreign-variable (num3 "num")
:type :int :accessor :address-of)
As a result, the next command returns a pointer to
num
, and to obtain the actual value stored by
num
,
num3
needs to be dereferenced.
(num3)
(fli:dereference (num3))