diff options
Diffstat (limited to 'ccan/container_of/container_of.h')
| -rw-r--r-- | ccan/container_of/container_of.h | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/ccan/container_of/container_of.h b/ccan/container_of/container_of.h index 6d1a5be8ac..ae3e1fc81f 100644 --- a/ccan/container_of/container_of.h +++ b/ccan/container_of/container_of.h @@ -33,6 +33,42 @@ - container_off(containing_type, member)) \ + check_types_match(*(member_ptr), ((containing_type *)0)->member)) + +/** + * container_of_or_null - get pointer to enclosing structure, or NULL + * @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, unless it + * is given NULL, in which case it also returns NULL. + * + * Example: + * struct foo { + * int fielda, fieldb; + * // ... + * }; + * struct info { + * int some_other_field; + * struct foo my_foo; + * }; + * + * static struct info *foo_to_info_allowing_null(struct foo *foo) + * { + * return container_of_or_null(foo, struct info, my_foo); + * } + */ +static inline char *container_of_or_null_(void *member_ptr, size_t offset) +{ + return member_ptr ? (char *)member_ptr - offset : NULL; +} +#define container_of_or_null(member_ptr, containing_type, member) \ + ((containing_type *) \ + container_of_or_null_(member_ptr, \ + container_off(containing_type, member)) \ + + check_types_match(*(member_ptr), ((containing_type *)0)->member)) + /** * container_off - get offset to enclosing structure * @containing_type: the type this member is within |