c - c中的可用内存问题删除了链表中的某些值

Question

typedef struct node_t { int val; struct node_t *next; } node;   

node *deleteNumber(node *node, int i) {
    while (node && node->val == i) {
        node = node->next;
    }
    n = node;
    p = node;
    if (n == NULL)
        return NULL;
    n = n->next;
    while (n) {
        if (n->val == i)
            p->next = n->next;
        else
            p = p->next;
        n = n->next;
    }
    return node;
}

我有一个问题，如何释放链表中已删除节点的内存。上面的函数，node是我要操作的链表，int是我要删除的值。谢谢!

它目前导致 valgrind 错误，我不知道从哪里开始。我试过 free(n,p) 但这没有帮助

> ==1618== 
> ==1618== HEAP SUMMARY:
> ==1618==     in use at exit: 192 bytes in 12 blocks
> ==1618==   total heap usage: 12 allocs, 0 frees, 192 bytes allocated
> ==1618== 
> ==1618== LEAK SUMMARY:
> ==1618==    definitely lost: 128 bytes in 8 blocks
> ==1618==    indirectly lost: 48 bytes in 3 blocks
> ==1618==      possibly lost: 0 bytes in 0 blocks
> ==1618==    still reachable: 16 bytes in 1 blocks
> ==1618==         suppressed: 0 bytes in 0 blocks
> ==1618== Rerun with --leak-check=full to see details of leaked memory
> ==1618== 
> ==1618== For counts of detected and suppressed errors, rerun with: -v
> ==1618== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Answer 1

我不完全确定你的 deleteNumber 应该做什么，但以下版本释放列表中与数字匹配的所有元素，返回指向剩余列表第一个元素的指针(如果列表现在为空，则为 NULL)。

#include <stdlib.h>

typedef struct node_t {   int val;   struct node_t *next; } node;

node* deleteNumber(node* start, int i) {
    node* n = start;
    node* p = NULL;
    node* t;

    while (n) {
        t = n;
        n = n->next;
        if (t->val == i) {
            if (p)
                p->next = n;
            else
                start = n;
            free(t);
        } else {
            p = t;
        }
    }
    return start;
}

下面是一些用于测试上述内容的附加函数:

#include <stdio.h>

/* append number to list, returning start of list */
node* addNumber(node* start, int i) {
    node* t;

    t = malloc(sizeof(*t));
    if (t == NULL)
        return start;
    t->next = NULL;
    t->val = i;
    if (start) {
        node* p = start;

        while (p->next)
            p = p->next;
        p->next = t;
    } else {
        start = t;
    }
    return start;
}

/* print elements of list */
void printList(node* list) {
    while (list) {
        printf(" %d", list->val);
        list = list->next;
    }
}

/* free whole list */
void deleteList(node* list) {
    node* t;

    while (list) {
        t = list;
        list = list->next;
        free(t);
    }
}

int main(void) {
    const int test[] = { 2, 3, 4, 2, 5 };
    node* start = NULL;
    int i;

    /* construct a list */
    for (i = 0; i < sizeof(test) / sizeof(test[0]); i++)
        start = addNumber(start, test[i]);
    /* report initial list contents */
    printf("Before:");
    printList(start);
    printf("\n");
    /* delete a number from the list */
    start = deleteNumber(start, 2);
    /* report updated list contents */
    printf("After:");
    printList(start);
    printf("\n");
    /* delete remaining elements of the list to appease Valgrind */
    deleteList(start);
    return 0;
}

上面的代码应该没有任何Valgrind错误。