x11/x11-base (->cstring): Convert 0 to the null pointer.

diff --git a/src/x11/x11-base.scm b/src/x11/x11-base.scm
index 8eb177e3fcc2d5e91792fba1cd8c800ae0ba284a..f30582fe5cdad1f8e506064bbb490a027d7951d5 100644 (file)
--- a/src/x11/x11-base.scm
+++ b/src/x11/x11-base.scm
@@ -70,23 +70,29 @@ Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
        #t)))
 
 (define (->cstring string)
-  (if (bytevector? string)
-      (if (let ((end (bytevector-length string)))
-           (let loop ((i 0))
-             (if (fix:< i end)
-                 (or (fix:zero? (bytevector-u8-ref string i))
-                     (loop (fix:1+ i)))
-                 #f)))
-         string
-         (error "C string not null terminated:" string))
-      ;; String->iso8859-1 would be incorrect here; it does not null terminate.
-      (let* ((end (string-length string))
-            (result (make-bytevector (fix:1+ end))))
-       (do ((i 0 (fix:1+ i)))
-           ((not (fix:< i end))
-            (bytevector-u8-set! result i #x00))
-         (bytevector-u8-set! result i (char->integer (string-ref string i))))
-       result)))
+  (cond ((and (integer? string) (zero? string))
+        0)
+       ((bytevector? string)
+        (if (let ((end (bytevector-length string)))
+              (let loop ((i 0))
+                (if (fix:< i end)
+                    (or (fix:zero? (bytevector-u8-ref string i))
+                        (loop (fix:1+ i)))
+                    #f)))
+            string
+            (error "C string not null terminated:" string)))
+       ((string? string)
+        ;; String->iso8859-1 would be incorrect; it does not null terminate.
+        (let* ((end (string-length string))
+               (result (make-bytevector (fix:1+ end))))
+          (do ((i 0 (fix:1+ i)))
+              ((not (fix:< i end))
+               (bytevector-u8-set! result i #x00))
+            (bytevector-u8-set! result i (char->integer
+                                          (string-ref string i))))
+          result))
+       (else
+        (error:wrong-type-argument string "a string or 0" '->cstring))))
 
 (define (x-window-set-name window name)
   (guarantee-xwindow window 'x-window-set-name)