4.1.2 Creating foreign structure types Examples

The code in the following example demonstrates how a foreign structure is defined and used. For more information about the function definitions, see Section 4.1.8 on page 113.

;;; STAT(2) fills in a structure that is defined as follows.  The
;;; C definition for this structure is found in the file <sys/
;;; stat.h>; it uses types defined in <sys/types.h> and <sys/
;;; time.h>. The (2) in the name of this function is a reference
;;; to the section of the UNIX manual pages in which the function
;;; is described. The descriptions are generally available on
;;; line.

> (def-foreign-struct timestruc (tv_sec :type :signed-32bit) (tv_nsec :type :signed-32bit)) TIMESTRUC

> (def-foreign-struct stat (st_dev :type :unsigned-32bit) ; device inode resides on (st_pad1 :type (:array :signed-32bit (3))) ; padding (st_ino :type :unsigned-32bit) ; this inode's number (st_mode :type :unsigned-32bit) ; protection ;; file's number of hard links (st_nlink :type :unsigned-32bit) (st_uid :type :signed-32bit) ; user id of owner (st_gid :type :signed-32bit) ; group id of owner (st_rdev :type :unsigned-32bit) ; type for device inode (st_pad2 :type (:array :signed-32bit (2))) ; padding (st_size :type :signed-32bit) ; total size of file (st_pad3 :type :signed-32bit) ; padding (st_atime :type timestruc) ; file's last access time ;; file's last modification time (st_mtime :type timestruc) ;; file's last status change time (st_ctime :type timestruc) ;; optimal block size for file system i/o operators (st_blksize :type :signed-32bit) ;; actual number of blocks allocated (st_blocks :type :signed-32bit) ;; file-system type name (st_fstype :type (:array :character (16))) (st_pad4 :type (:array :signed-32bit (8)))) STAT

;;; LIBC-STAT is a direct translation of the libc declaration for ;;; STAT(2): ;;; int stat(path, buf) ;;; char *path; ;;; struct stat *buf;

> (def-foreign-function (libc-stat (:return-type :signed-32bit) (:name "stat") (:language :c)) (path (:pointer :character)) (buf (:pointer stat))) LIBC-STAT

;; The Lisp function STAT returns a list containing the ;; information that STAT(2) returns about the file named path, a ;; Lisp string. If STAT(2) fails, STAT returns NIL. (If STAT(2) ;; succeeds, it returns 0; otherwise, it returns -1 and sets ;; errno.) Like the GETENV example in ;; Section 4.1.1, ;; STAT calls LIBC-STAT with a ;; foreign storage copy of path and reclaims the foreign storage ;; that it uses.

> (defun stat (path) (check-type path string) ;; MALLOC-FOREIGN-STRING is defined in the GETENV example in ;; Section 4.1.1. (let ((f-path (malloc-foreign-string path)) (buf (malloc-foreign-pointer :type '(:pointer stat)))) ;; After copying path into foreign storage and allocating ;; a buffer for the file information, call STAT(2) (via ;; LIBC-STAT). If the call fails, return NIL; otherwise, ;; return a list with the file information. In either case, ;; reclaim the foreign storage used.

(prog1 (if (not (zerop (libc-stat f-path buf))) '() (list (stat-st_dev buf) (stat-st_ino buf) (stat-st_mode buf) (stat-st_nlink buf) (stat-st_uid buf) (stat-st_gid buf) (stat-st_rdev buf) (stat-st_size buf) (timestruc-tv_sec (stat-st_atime buf)) (timestruc-tv_sec (stat-st_mtime buf)) (timestruc-tv_sec (stat-st_ctime buf)) (stat-st_blksize buf) (stat-st_blocks buf) (delete #\\Null (foreign-string-value (stat-st_fstype buf))))) (free-foreign-pointer f-path) (free-foreign-pointer buf)))) STAT

> (stat "/") (8388632 2 16877 25 0 0 0 4096 724450613 724450659 724450659 8192 8 "ufs")

> (stat "/dev") (8388632 6113 16893 15 0 3 0 4608 724445861 724386895 724386895 8192 10 "ufs")

> (stat "/dev/tty") (8388632 2474 8630 1 0 3 5767168 0 721631236 721631236 721687093 8192 0 "ufs")

The Advanced User's Guide - 9 SEP 1996

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