+/* CC0 (Public domain) - see LICENSE file for details */
#ifndef CCAN_CONTAINER_OF_H
#define CCAN_CONTAINER_OF_H
#include <stddef.h>
#define container_of_var(member_ptr, container_var, member) \
container_of(member_ptr, typeof(*container_var), member)
#else
-#define container_of_var(member_ptr, container_var, member) \
- ((void *)((char *)(member_ptr) \
- - ((char *)&(container_var)->member \
- - (char *)(container_var))))
+#define container_of_var(member_ptr, container_var, member) \
+ ((void *)((char *)(member_ptr) - \
+ container_off_var(container_var, member)))
+#endif
+
+/**
+ * container_off_var - get offset of a field in enclosing structure
+ * @container_var: a pointer to a container structure
+ * @member: the name of a member within the structure.
+ *
+ * Given (any) pointer to a structure and a its member name, this
+ * macro does pointer subtraction to return offset of member in a
+ * structure memory layout.
+ *
+ */
+#if HAVE_TYPEOF
+#define container_off_var(var, member) \
+ container_off(typeof(*var), member)
+#else
+#define container_off_var(var, member) \
+ ((const char *)&(var)->member - (const char *)(var))
#endif
#endif /* CCAN_CONTAINER_OF_H */