Question

注意：我无法使用＆＃39;。＆＃39;和＆＃39; - ＆gt;＆＃39;图上的运算符。这就是我使用这些宏的原因。

对于以下图表声明（我无法更改 - 作业，所以请不要问我任何相关内容），

#include <stdio.h>
#include <stdlib.h>
#define TAG(vp)   ((vp)->tag)
#define LABEL(vp) ((vp)->label)  
#define EDGE(vp)  ((vp)->edge)

typedef struct vertex 
{
    char tag; /* can be used for any puproses; haven't used though */
    char *label;
    struct vertex *edge[1];
}
vertex, *vp;

我编写了以下结构和函数，为图形创建邻接列表。

typedef struct adjList
{
    vp node;
    struct adjList *next;
}
adjList;


void createList (adjList *list, vp graph, int *place) /* place stores an index in an array of adjacency lists */
{
    int i, temp = *place;
    adjList *ptr;
    if (graph)
    {
        list[temp].node = graph;
        list[temp].next = NULL;
        if (EDGE (graph))
        {
            ptr = list[temp].next;
            for (i = 0; EDGE (graph)[i]; ++i)
            {
                ptr = malloc (sizeof (adjList));
                ptr->node = EDGE (graph)[i];
                ptr = ptr->next;
            }
        }
        ++(*place);
        list = realloc (list, sizeof (adjList) * (*place + 1));
        for (i = 0; EDGE (graph)[i]; ++i)
        {
            createList (list, EDGE (graph)[i], place);
        }
    }
}

使用这个main，我得到了一个分段错误。

int main()
{
    int i;
    int *temp = malloc (sizeof (int));
    adjList *list, *ptr;
    vp test;
    *temp = 0; /* temp is an index starting from 0 */
    test = malloc (sizeof (*test) + 4 * sizeof (vp));
    list = malloc (sizeof (adjList));
    LABEL (test) = malloc (sizeof (char));
    LABEL (test)[0] = 'a';
    for (i = 0; i < 3; ++i)
    {
        EDGE (test)[i] = malloc (sizeof (vertex));
    }
    LABEL (EDGE (test)[0]) = malloc (sizeof (char));
    LABEL (EDGE (test)[0])[0] = 'b';
    LABEL (EDGE (test)[1]) = malloc (sizeof (char));
    LABEL (EDGE (test)[1])[0] = 'c';
    LABEL (EDGE (test)[2]) = malloc (sizeof (char));
    LABEL (EDGE (test)[2])[0] = 'd';
    EDGE (EDGE (test)[0])[0] = NULL;
    EDGE (EDGE (test)[1])[0] = NULL;
    EDGE (EDGE (test)[2])[0] = NULL;
    EDGE (test)[3] = NULL;
    printf ("%d\n", sizeof (EDGE (test)) / sizeof (vp));
    createList (list, test, temp);
    list = realloc (list, sizeof (adjList) * (*temp));
    printf ("%c\n", LABEL (test)[0]);
    printf ("%d\n", (test == list[0].node));
    for (ptr = list; ptr; ptr = ptr->next)
    {
        printf ("%c ", LABEL (ptr->node)[0]);
    }
    printf ("\n");
    return 0;
}

在调试时，我发现创建邻接列表的函数甚至不会将指针存储在＆＃34; adjList＆＃34;结构。也许我没有正确分配内存。任何一点帮助将不胜感激。

提前致谢。

Answer 1

在Mac OS X上运行，我收到消息：

graph(70806) malloc: *** error for object 0x7fb211c03b20: pointer being realloc'd was not allocated

使用createList()函数的注释版本：

static
void createList (adjList *list, vp graph, int *place) /* place stores an index in an array of adjacency lists */
{
    int i, temp = *place;
    adjList *ptr;
    if (graph)
    {
        printf("-->> %s()\n", __func__);
        list[temp].node = graph;
        list[temp].next = NULL;
        if (EDGE (graph))
        {
            ptr = list[temp].next;
            for (i = 0; EDGE (graph)[i]; ++i)
            {
                ptr = malloc (sizeof (adjList));
                ptr->node = EDGE (graph)[i];
                ptr = ptr->next;
            }
        }
        ++(*place);
        printf("About to realloc() in createList()\n");
        list = realloc (list, sizeof (adjList) * (*place + 1));
        printf("Back from realloc() in createList()\n");
        for (i = 0; EDGE (graph)[i]; ++i)
        {
            printf("Recursing in createList\n");
            createList (list, EDGE (graph)[i], place);
            printf("Back from recursive createList\n");
        }
        printf("<<-- %s()\n", __func__);
    }
}

运行的输出是：

1
-->> createList()
About to realloc() in createList()
Back from realloc() in createList()
Recursing in createList
-->> createList()
About to realloc() in createList()
Back from realloc() in createList()
<<-- createList()
Back from recursive createList
Recursing in createList
-->> createList()
About to realloc() in createList()
graph(70904) malloc: *** error for object 0x7fefca403b20: pointer being realloc'd was not allocated
*** set a breakpoint in malloc_error_break to debug

问题是createList()重新分配传入的list，但无法告诉调用代码新列表的地址。您需要修改createList()以返回新列表，或安排将adjList **list传递给函数 - 在任何一种情况下都会随之发生变化。

C：来自图 - 分段故障的邻接列表

1 个答案: