Question

我正在尝试创建一个从队列中弹出元素的函数

/**
 * This function extracts from the queue the patient with maximum priority
 * @param queue is the extraction point
 * @return the patient with maximum priority or a Patient type value with all the fields 0 if the queue is empty
 */

struct Patient priorityQueuePop(struct PriorityQueue *queue);

结构PriorityQueue是这样的：

struct PriorityQueue{
    unsigned size;
    struct PriorityQueue *next;
    struct PriorityQueue *front;
    struct PriorityQueue *rear;
}

患者就是这样：

enum Gender {
    MALE = 'M',
    FEMALE = 'F'
};

struct Patient {
    char firstName[20];
    char lastName[20];
    unsigned char age;
    enum Gender gender;
};

我试着做这样的事情：

struct Patient priorityQueuePop(struct PriorityQueue *queue){

struct Patient *item =(struct Patient*)malloc(sizeof(struct Patient));

    queue->front = queue->front->next;
    queue->size--;

return item;
}

但编译时出错：

priorityQueue.c:72:2: error: incompatible types when returning type ‘struct Patient *’ but ‘struct Patient’ was expected
return item;

有人可以解释如何做到这一点吗？谢谢

Answer 1

假设你的pop功能有正确的签名。

struct Patient priorityQueuePop(struct PriorityQueue *queue);

这表示函数priorityQueuePop应返回struct Patient。这与struct Patient *不同。

struct Patient a_patient;
struct Patient *a_pointer_to_a_patient;

你如何归还结构？您无需动态分配它。

struct Patient
priorityQueuePop(struct PriorityQueue *queue)
{
    struct Patient patient;
    struct PriorityQueue *item;

    item = queue->front
    queue->front = queue->front->next;
    queue->size -= 1;
    if (queue->size == 0) {
        queue->front = queue->rear = queue->next = NULL;
    }
    item->front = item->rear = item->next = NULL;
    populatePatientFromItem(&patient, item);
    priorityQueueDestroy(item);

    return patient;
}

请注意，虽然理论上认为优先级队列的 cdr 也是优先级队列是正确的，但在这种情况下它是过度的，因为它看起来你的接口没有在利用它的方式。

链接列表队列[pop功能]

1 个答案: