CIRCLEQ_FOREACH_REVERSE - Linux

Overview

The CIRCLEQ_FOREACH_REVERSE macro iterates over a circular doubly linked list in reverse order. It is commonly used to traverse the list from the last element to the first.

Syntax

#include <sys/queue.h>

CIRCLEQ_FOREACH_REVERSE(var, head, field)

Parameters

• var: A variable to store each entry found in the list as it is iterated.
• head: The head element of the circular doubly linked list.
• field: The name of the field within each entry that contains the next entry in the list.

Options/Flags

There are no options or flags available for CIRCLEQ_FOREACH_REVERSE.

Examples

Iterating Over a List in Reverse Order

The following example shows how to iterate over a circular doubly linked list in reverse order:

#include <sys/queue.h>

struct entry {
    CIRCLEQ_ENTRY(entry) entries;
    int value;
};

int main() {
    struct entry *head = NULL;

    CIRCLEQ_INSERT_HEAD(head, entry1, entries);
    CIRCLEQ_INSERT_HEAD(head, entry2, entries);
    CIRCLEQ_INSERT_HEAD(head, entry3, entries);

    CIRCLEQ_FOREACH_REVERSE(entry, head, entries) {
        printf("%d\n", entry->value);
    }

    return 0;
}

Output:

3
2
1

Common Issues

One common issue when using CIRCLEQ_FOREACH_REVERSE is ensuring that the circular doubly linked list is properly initialized. The head element must be set to NULL before inserting any entries into the list.

Integration

CIRCLEQ_FOREACH_REVERSE can be used in conjunction with other circular doubly linked list macros, such as CIRCLEQ_INSERT_HEAD and CIRCLEQ_REMOVE, to manipulate circular doubly linked lists efficiently.

Related Commands

• CIRCLEQ_FOREACH: Iterates over a circular doubly linked list in forward order.
• CIRCLEQ_INIT: Initializes a circular doubly linked list.
• CIRCLEQ_INSERT_HEAD: Inserts a new entry at the head of a circular doubly linked list.
• CIRCLEQ_REMOVE: Removes an entry from a circular doubly linked list.