C 循环链表答案

【问题标题】：C Circular Linked listC 循环链表
【发布时间】：2020-06-28 04:21:15
【问题描述】：

您好，我最近刚刚在 Java 中实现了一个循环链表，但在 (C) 编程语言中这样做时遇到了一些麻烦 - 没有条目将打印到控制台。有人可以帮我处理循环链表的插入和输出部分吗？

这里是插入函数以及输出函数。

/**
 *  FUNCTION        :   addWeapon
 *  DESCRIPTION     :   This function will add a new weapon to the weapon wheel.
 *  PARAMETERS      :   pWeaponHead
 *  RETURNS         :   true, false
 */
const bool addWeapon(struct Weapon* pWeaponHead, struct Weapon* pWeaponTail)
{
    struct Weapon* pNewWeapon = NULL;
    pNewWeapon = (struct Weapon*)malloc(sizeof(struct Weapon));

    // Check the system for sufficient memory.
    if (pNewWeapon == NULL) { return false; }
    else
    {
        // We have memory for a new weapon entry.
        getchar();
        printf(KPROMPTFORWEAPON);
        fgets(pNewWeapon->arsWeapon, K100BYTES, stdin);
        newLineRemover(pNewWeapon->arsWeapon);
        pNewWeapon->pNext = pNewWeapon;

        // Is the weapon wheel empty ?
        if (pWeaponHead == NULL) 
        {
            pWeaponHead = pNewWeapon;
            pWeaponTail = pNewWeapon;
            return true;
        }
        pWeaponTail->pNext = pWeaponHead;
        pNewWeapon->pNext = pNewWeapon;
        pWeaponHead = pNewWeapon;
    }
    return true;
}

/**
 *  FUNCTION        :   showWeaponWheel
 *  DESCRIPTION     :   This function will display the weapon selection
 *                      which is represented by the "Weapon Wheel" this allows
 *                      us to choose which weapon we would like that exists in the list.
 *  PARAMETERS      :   pWeaponHead
 *  RETURNS         :   true, false
 */
const bool showWeaponWheel(struct Weapon* pWeaponHead)
{
    // Check to see if the list is empty.
    if (pWeaponHead == NULL) { return false; }

    struct Weapon* pHead = pWeaponHead;
    printf("** -- Weapon Wheel -- \n");
    do
    {   
        printf("\t%s\n", pHead->arsWeapon);
        pHead = pHead->pNext;
    } while (pHead != pWeaponHead);
    return true;
}

【问题讨论】：

这段代码你遇到了什么问题？无法按预期工作或程序崩溃或其他原因？
@kiner_shah 没有条目将打印到控制台。
函数问题中的标准设置指针。 WeaponHead = pNewWeapon 设置 local 变量。调用者的变量没有改变。该函数需要返回头指针或需要传入双指针。
@kaylum 一个问题：你能传入一个双指针并返回 void 吗？
这能回答你的问题吗？ Changing address contained by pointer using function

标签： c circular-list

【解决方案1】：

似乎有两个问题... 首先，如 cmets 中所述，您已经传递了指针的值并尝试更改它，这不会更改实际指针的值。您需要将该指针的地址作为双指针传递。这将帮助您添加第一个条目。其次，我不明白

        pWeaponTail->pNext = pWeaponHead;
        pNewWeapon->pNext = pNewWeapon;
        pWeaponHead = pNewWeapon;

它只是将尾部链接到列表的头部，并将新条目的尾部链接到自身..它不会工作

试试这个：

const bool addWeapon(struct Weapon** pWeaponHead, struct Weapon** pWeaponTail)
{
    struct Weapon* pNewWeapon = NULL;
    pNewWeapon = (struct Weapon*)malloc(sizeof(struct Weapon));

    // Check the system for sufficient memory.
    if (pNewWeapon == NULL) { return false; }
    else
    {
        // We have memory for a new weapon entry.
        getchar();
        printf(KPROMPTFORWEAPON);
        fgets(pNewWeapon->arsWeapon, K100BYTES, stdin);
        newLineRemover(pNewWeapon->arsWeapon);
        pNewWeapon->pNext = pNewWeapon;

        // Is the weapon wheel empty ?
        if (*pWeaponHead == NULL) 
        {
           *pWeaponHead = pNewWeapon;
           *pWeaponTail = pNewWeapon;
            return true;
        }
        (*pWeaponTail)->pNext = pNewWeapon;
        pNewWeapon->pNext = *pWeaponHead;
        *pWeaponHead = pNewWeapon;
    }
    return true;
}

【讨论】：