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ccan/container_of: add container_of_or_null

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* ccan/container_of/container_of.h (container_of_or_null): added
  [ccan 7ec5b8e06b2fd5fa98b1fcde1158c286d2d429d8] (David Gibson)

It's quite common to have a pointer which could be either a pointer to a
structure member, or NULL.  This needs special casing with container_of(),
or it will convert NULL into something strange.

This patch adds container_of_or_null(), which will return NULL if passed
(an appropriately typed) NULL, or the containining structure as
container_of() otherwise.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47579 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
This commit is contained in:
normal 2014-09-13 23:49:28 +00:00
parent a5fc33c0e2
commit e7f6d9e25a
2 changed files with 41 additions and 0 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
Sun Sep 14 08:43:37 2014 Eric Wong <e@80x24.org>
* ccan/container_of/container_of.h (container_of_or_null): added
[ccan 7ec5b8e06b2fd5fa98b1fcde1158c286d2d429d8] (David Gibson)
Sun Sep 14 08:41:44 2014 Eric Wong <e@80x24.org>
* ccan/list/list.h (list_del_init, list_node_init): new functions

36
ccan/container_of/container_of.h
View file

@ -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