8.3.3 Alien Dynamic Allocation

Dynamic Aliens are allocated using the malloc library, so foreign code can call free on the result of make-alien, and Lisp code can call free-alien on objects allocated by foreign code.

[Macro]
alien: make-alien type size

This macro returns a dynamically allocated Alien of the specified type (which is not evaluated.) The allocated memory is not initialized, and may contain arbitrary junk. If supplied, size is an expression to evaluate to compute the size of the allocated object. There are two major cases:

• When type is an array type, an array of that type is allocated and a pointer to it is returned. Note that you must use deref to change the result to an array before you can use deref to read or write elements:

  (defvar *foo* (make-alien (array char 10)))
  
        (type-of *foo*)  (alien (* (array (signed 8) 10)))
  
        (setf (deref (deref foo) 0) 10)  10
      

  If supplied, size is used as the first dimension for the array.
• When type is any other type, then then an object for that type is allocated, and a pointer to it is returned. So (make-alien int) returns a (* int). If size is specified, then a block of that many objects is allocated, with the result pointing to the first one.

[Function]
alien: free-alien alien

This function frees the storage for alien (which must have been allocated with make-alien or malloc.)

See also  with-alien (page ), which stack-allocates Aliens.