C:图中的邻接列表 - 段错误

Question

注意:我不能使用“.”和图表上的“->”运算符。这就是我使用这些宏的原因。

对于以下图形声明(我无法更改 - 赋值，所以请不要问我任何相关问题)，

#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来为图创建邻接列表。

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 时，我遇到了段错误。

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;
}

在调试它时，我发现创建邻接列表的函数甚至没有在“adjList”结构中存储指针。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

使用这个带注释的 createList() 函数版本:

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

问题在于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，或者安排将 adjList **list 传递到函数中 - 无论哪种情况，都会进行相应的更改.