我想在 C 中的堆插入函数中使用 realloc。这是代码:
typedef struct MaxHeap {
int size;
int* heap;
} MaxHeap;
void max_insert(MaxHeap* max_heap, int* key_index, int key) { // O(logn)
max_heap->heap = realloc((max_heap->size+1), sizeof * max_heap->heap);
max_heap[max_heap->size] = N_INF;
max_heap->size += 1;
increase_key(max_heap, key_index, max_heap->size, key)
}
我收到这个警告:
warning: passing argument 1 of ‘realloc’ makes pointer from integer without a cast [-Wint-conversion]
我尝试了这个修复:
max_heap->heap = realloc((max_heap->heap), (max_heap->size+1) * sizeof(*(max_heap->heap)));
更新
我这样做了:
void max_insert(MaxHeap* max_heap, int* key_index, int key) { // O(logn)
int* temp = realloc (max_heap->heap, (max_heap->size + 1) * sizeof (*(max_heap->heap)));
if (!temp) exit(1);
max_heap->heap = temp;
max_heap->heap[max_heap->size] = N_INF;
max_heap->size += 1;
increase_key(max_heap, key_index, max_heap->size, key);
temp = 0;
}
我得到了这个错误
realloc(): invalid old size
您已将参数交换为
realloc()
.
(max_heap->size+1)
评估为
int
,但 realloc()
的第一个参数需要一个 void *
指针。替换为:
(max_heap->heap);
对
realloc()
的调用变成:
realloc (max_heap->heap, (max_heap->size + 1) * sizeof (*(max_heap->heap)));
请注意,这失败有两个原因:
realloc()
返回NULL
,这将被忽视,因为我们没有检查realloc()
的返回值。后续操作现在将写入/取消引用/读取NULL
,这将调用未定义的行为。realloc()
返回NULL
,我们将无法访问原始内存,这将导致内存泄漏。修复:
使用临时指针保存
realloc()
的返回值:
int *tmp = realloc (... , ...);
if (!tmp) {
perror ("realloc()");
/* realloc() was unable to allocate memory.
* The original memory is left untouched.
* Handle error here.
*/
}
/* Now we can assign the result to `max_heap->heap`: */
max_heap->heap = tmp;
tmp = 0; /* This is unnecessary, but eliminates a dangling pointer. */