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.Dd October 8, 2011
.Dt CONTAINER_OF 3
.Os
.Sh NAME
.Nm container_of
.Nd cast a pointer to member of a structure to a pointer of its
container structure.
.Sh SYNOPSIS
.In sys/container_of.h
.Ft "type *"
.Fn container_of "pointer" "type" "member"
.Sh DESCRIPTION
Given a
.Fa pointer
that points to a
.Fa member
of the container structure
.Fa type
the
.Fn container_of
macro returns a pointer that points to the enclosing container structure.
.Pp
A compiler error will result if
.Ar member
is not aligned to a byte boundary
.Pq i.e. it is a bit-field .
.Sh EXAMPLES
.Bd -literal
#include <assert.h>
#include <sys/container_of.h>
struct container {
        double  other_member;
        int     member;
};

struct container one;

void test(void) {
        int *ptr = &one.member;
        struct container *onep = container_of(ptr, struct container, member);
        assert(onep == &one);
}
.Ed
.Sh SEE ALSO
.Xr __alignof__ 3 ,
.Xr offsetof 3 ,
.Xr stddef 3 ,
.Xr typeof 3
.Sh HISTORY
The
.Fn container_of
macro appeared first in the Linux kernel.