CIRCLEQ_PREV - Linux

Overview

CIRCLEQ_PREV is a Linux utility used for manipulating circular doubly linked lists in C programs. It returns the previous node in the circular queue.

Syntax

#include <sys/queue.h>
CIRCLEQ_PREV(node, type, field_name);

where:

  • node is the current node of the circular queue.
  • type is the data type of the nodes.
  • field_name is the name of the field within the node that contains the pointer to the next node.

Options/Flags

This command does not have any configurable options or flags.

Examples

To get the previous node in a circular queue:

struct node {
    CIRCLEQ_ENTRY(node) entries;
    int data;
};

CIRCLEQ_HEAD(queue_head, node);

struct queue_head *queue = ...;
struct node *current_node = ...;

struct node *previous_node = CIRCLEQ_PREV(current_node, node, entries);

Common Issues

  • Type mismatch: Ensure that the type specified in the CIRCLEQ_PREV macro matches the actual data type of the nodes.
  • Invalid node: Verify that the current_node argument is a valid node within the circular queue.

Integration

CIRCLEQ_PREV can be used in conjunction with other circular queue operations, such as CIRCLEQ_INSERT_BEFORE and CIRCLEQ_REMOVE. This allows for complex circular queue manipulations and data processing.

Related Commands

  • CIRCLEQ_FIRST: Return the first node in the circular queue.
  • CIRCLEQ_LAST: Return the last node in the circular queue.
  • CIRCLEQ_NEXT: Return the next node in the circular queue.
  • CIRCLEQ_INSERT_BEFORE: Insert a node before the specified node in the circular queue.
  • CIRCLEQ_REMOVE: Remove a node from the circular queue.