无法在C中返回多维数组

I'm trying to write a function in C, which returns the pointer to an array. Each element of this array is a pointer to the initialized structure, and in each structure there's also a pointer to an array.

我正在尝试用C编写一个函数，它返回指向数组的指针。该数组的每个元素都是指向初始化结构的指针，并且在每个结构中还有一个指向数组的指针。

struct queueRecord;
typedef struct queueRecord* queue;

queue createQueue(int maxSize){
    queue newQueue = malloc(sizeof(struct queueRecord));
    newQueue->array = malloc(sizeof(int)*maxSize);
    newQueue->capacity=maxSize;
    newQueue->front=0;
    newQueue->rear=0;
    return newQueue;
}

This just works fine as well as in the following function:

这只是工作正常以及以下功能：

queue* initQArr(int maxSize){
    queue arr[10];
    for (int i=0; i<10; i++) {
        arr[i]=createQueue(maxSize);
    }
    return arr;
}

when I pass the parameter 10 in it and set a breakpoint at return, everything seems good (excuse me I can't post images, the debug information is like following):

当我在其中传递参数10并在返回时设置断点时，一切似乎都很好（请原谅我无法发布图像，调试信息如下）：

arr(queue[10])
 [0]=(queue)0x100105480
   capacity=(int)10
   size=(int)0
   front=(int)0
   rear=(int)0
   array=(int*)0x1001054a0
 [1]=(queue)0x1001054d0
 ...
 ...
 [9]=(queue)0x100105760

However!When I invoke this function and return to a new array, I got an array with only 5 elements:

但是！当我调用这个函数并返回一个新数组时，我得到一个只有5个元素的数组：

queue *digitsQArr = initQArr(length);
int digit = 0;

(debug information as following):

（调试信息如下）：

digitQArr = (queue*)0x7fff5fbff6d0
    *digitsArr=(queue)0x100105480
        capacity=(int)10
        size=(int)0
        front=(int)0
        rear=(int)0
        array=(int*)0x1001054a0
    [1]=(queue)0x1001054d0
    ...
    ...
    [4]=(queue)0x1001055d0

1 个解决方案

#1

In initQArr, you return the address of a local variable, arr:

在initQArr中，返回局部变量的地址，arr：

queue* initQArr(int maxSize){
    queue arr[10];
    for (int i=0; i<10; i++) {
        arr[i]=createQueue(maxSize);
    }
    return arr;
}

The returned pointer will point to the local array arr, which is no longer valid once the function returns. You could follow the example of createQueue and allocate memory on the heap:

返回的指针将指向本地数组arr，该函数返回后不再有效。您可以按照createQueue的示例并在堆上分配内存：

queue* initQArr(int maxSize){
    queue *arr = malloc(10 * sizeof(*arr));
    for (int i=0; i<10; i++) {
        arr[i]=createQueue(maxSize);
    }

    return arr;
}

After returning, the pointer arr is still valid, because it points to memory on the heap. You should free such memory after using it, like the queue pointers allocated in createQueue.

返回后，指针arr仍然有效，因为它指向堆上的内存。你应该在使用它之后释放这样的内存，就像在createQueue中分配的队列指针一样。

#1