ccan/ccan/container_of/container_of.h

#ifndef CCAN_CONTAINER_OF_H
#define CCAN_CONTAINER_OF_H
#include <stddef.h>

#include "config.h"
#include <ccan/check_type/check_type.h>

/**
 * container_of - get pointer to enclosing structure
 * @member_ptr: pointer to the structure member
 * @containing_type: the type this member is within
 * @member: the name of this member within the structure.
 *
 * Given a pointer to a member of a structure, this macro does pointer
 * subtraction to return the pointer to the enclosing type.
 *
 * Example:
 *	struct foo {
 *		int fielda, fieldb;
 *		// ...
 *	};
 *	struct info {
 *		int some_other_field;
 *		struct foo my_foo;
 *	};
 *
 *	static struct info *foo_to_info(struct foo *foo)
 *	{
 *		return container_of(foo, struct info, my_foo);
 *	}
 */
#define container_of(member_ptr, containing_type, member)		\
	 ((containing_type *)						\
	  ((char *)(member_ptr) - offsetof(containing_type, member))	\
	  - check_types_match(*(member_ptr), ((containing_type *)0)->member))


/**
 * container_of_var - get pointer to enclosing structure using a variable
 * @member_ptr: pointer to the structure member
 * @var: a pointer to a structure of same type as this member is within
 * @member: the name of this member within the structure.
 *
 * Given a pointer to a member of a structure, this macro does pointer
 * subtraction to return the pointer to the enclosing type.
 *
 * Example:
 *	static struct info *foo_to_i(struct foo *foo)
 *	{
 *		struct info *i = container_of_var(foo, i, my_foo);
 *		return i;
 *	}
 */
#ifdef HAVE_TYPEOF
#define container_of_var(member_ptr, var, member) \
	container_of(member_ptr, typeof(*var), member)
#else
#define container_of_var(member_ptr, var, member) \
	((void *)((char *)(member_ptr) - offsetof(containing_type, member)))
#endif

#endif /* CCAN_CONTAINER_OF_H */