How is container_of utilized?

1 year ago
Liam
2 minutes

“container_of is a C language macro used to obtain a pointer to the structure containing a specific member by using a pointer to that member.”

Here is how to use it:

#define container_of(ptr, type, member) \
    ((type *)((char *)(ptr) - offsetof(type, member)))

Explanation of parameters:

  1. ptr: pointer to a member of a structure.
  2. type: the type of the structure.
  3. Member: The name of a member within a structure.

The container_of macro calculates the offset of a member within a structure using the offsetof macro, then subtracts the offset from the member pointer to obtain a pointer to the structure.

Here is an example of using the container_of macro:

#include <stddef.h>

struct Person {
    char name[20];
    int age;
};

int main() {
    struct Person p = {"John Doe", 25};
    int *p_age = &p.age;

    struct Person *p_ptr = container_of(p_age, struct Person, age);

    printf("Name: %s\n", p_ptr->name);
    printf("Age: %d\n", p_ptr->age);

    return 0;
}

Output result:

Name: John Doe
Age: 25

In the example above, using the container_of macro, we can obtain a pointer to the struct Person containing the member p.age by accessing p_ptr through the pointer p_age, allowing us to access other members of the struct.

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