container_of

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Name

container_of - obtain a pointer to the struct that contains the struct member

Synopsis

#include "container_of.h"

container_of(member_pointer, containing_struct, struct_member);

Description

The container_of() macro returns a pointer to the struct that contains this struct member.

This is useful if you have an API that passes a pointer to only the struct member. You can use this macro to obtain a pointer to the struct that contains that pointer.

member_pointer is a pointer to a member of container_struct. container_struct is the type of the struct that contains the member. struct_member is the literal of the member's name within container_struct.

Return Value

A pointer to the struct that contains this member.

Example

.. code-block:: c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "container_of.h"

typedef struct {
    char* name;
    int cash;
} account_t;

void deposit(int* current_balance, int change)
{
    account_t* acc = container_of(current_balance, account_t, cash);
    printf("Increased %s's account by %d\n", acc->name, change);
}

int main()
{
    account_t *acc = calloc(1, sizeof(account_t));
    acc->name = strdup("Alice");
    deposit(&acc->cash, 100);
}

Further reading

http://broken.build/2012/11/10/magical-container_of-macro/ http://stackoverflow.com/questions/15832301/understanding-container-of-macro-in-linux-kernel http://www.linuxjournal.com/files/linuxjournal.com/linuxjournal/articles/067/6717/6717s2.html http://www.kroah.com/log/linux/container_of.html http://en.wikipedia.org/wiki/Offsetof