0 
typedef struct ArrayList
{
    // We will store an array of strings (i.e., an array of char arrays)
    char **array;

    // Size of list (i.e., number of elements that have been added to the array)
    int size;

    // Length of the array (i.e., the array's current maximum capacity)
    int capacity;

} ArrayList;

The following function is supposed to dynamically allocate memory for an array of strings supported by a header file which contains a struct (see above):

void panic(char *s)
{
    fprintf(stderr, "%s", s);
    exit(1);
}

ArrayList *createArrayList(int length){
    ArrayList *n = malloc(sizeof(ArrayList));

    int initial = 0, i;

    if (length > DEFAULT_INIT_LEN)
    {
        n->array = (char **)malloc(length * sizeof(int*));
        n->capacity = length;

        for (i = 0; i< n->capacity; i++)
        {
            n->array[i] = NULL;
        }
    }
    else
    {
        n->array = (char **)malloc(DEFAULT_INIT_LEN * sizeof(int*));
        n->capacity = DEFAULT_INIT_LEN;

        for (i = 0; i< n->capacity; i++)
        {
            n->array[i] = NULL;
        }
    }

    if (n->array == NULL)
        panic("ERROR: out of memory in Mylist!\n");

    n->size = initial;

    printf("-> Created new ArrayList of size %d\n", n->capacity);
    return n;
}

Then I have another function that is supposed to print all of the strings currently in the newly allocated array created by the createArrayList function:

void printArrayList(ArrayList *list)
{
    int i;

    for(i=0; i<list->capacity; i++)
    {
        if (list->array[i] == NULL)
            printf("(empty list)\n");
        else
            printf("%s\n",list->array[i]);

    }
}

When I implement the printArrayList function (above) in my main function, the output is:

-> Created ArrayList of size 10 
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)

However, if i insert strcpy(n->array[1], "apple"); in the createArrayList function as a means of testing the 2D array's ability to hold strings the output is:

-> Created ArrayList of size 10

...and then it crashes

So my question is what am I doing wrong? Am I incorrectly allocating memeory for my array? I want to get it so the output is:

-> Created ArrayList of size 10 
(empty list)
apple
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
(empty list)
4

2 回答 2

1

除了为 分配内存ArrayList外，您还需要为每个字符串分配存储空间。如果要设置数组的第二个元素，可以使用类似

void insert_at(ArrayList* arraylist, const char* str, int index)
{
    arraylist->array[index] = malloc(strlen(str)+1);
    if (arraylist->array[index] != NULL) {
        strcpy(arraylist->array[index], str);
    }
}

并称它为

insert_at(n, 1, "apple");

顺便说一句，你的代码喜欢

n->array = (char **)malloc(length * sizeof(int*));

应该

n->array = malloc(length * sizeof(char*));

char（它是一个指向而不是指针的数组，int你不应该从mallocC 中转换返回）

于 2013-05-27T18:59:55.217 回答
0

3个问题

1）小：变化

n->array = (char **)malloc(length * sizeof(int*));

至

n->array = (char **)malloc(length * sizeof(char*));

2）把你的直接测试放在if (n->array == NULL)后面n->array = (char **)malloc(...

n->array = (char **)malloc(DEFAULT_INIT_LEN * sizeof(int*));
if (n->array == NULL)
   panic("ERROR: out of memory in Mylist!\n");

3) 最重要的。你不能不先strcpy(n->array[1], "apple");分配内存n->array[1]。就像是

n->array[1] = malloc(strlen("Fred")+1);
strcpy(n->array[1], "Fred");
于 2013-05-27T19:05:21.613 回答