c++ - C++中括号在指针数组中的作用

Question

尝试使用 this 实现图形链接，我遇到了严重的语法疑问。

/ A structure to represent an adjacency list node
struct AdjListNode
{
    int dest;
    struct AdjListNode* next;
};

// A structure to represent an adjacency liat
struct AdjList
{
    struct AdjListNode *head;  // pointer to head node of list
};

// A structure to represent a graph. A graph is an array of adjacency lists.
// Size of array will be V (number of vertices in graph)
struct Graph
{
    int V;
    struct AdjList* array;
};

在我上面提到的，它是用 C 实现的，而我用 C++ 实现了它。现在是创建图形数据结构的函数:

struct Graph* createGraph(int V) {
  struct Graph *graph;
  graph = new (struct Graph);
  graph->V = V;

  //the problem line below   
  graph->array = new (struct AdjList)[V];
  //initialize all the elements in the array as NULL
  for(int i = 0; i < V ; i++) {
    graph->array[i].head = NULL;
  }
  return graph;
}

此代码给出错误:array bound forbidden after parenthesized type-id而如果我只是从问题行中删除 paranthese，一切正常。为什么会这样？

编辑:

我知道如何解决这个问题。只需要这样做。

graph->array = new struct AdjList[V];

问题是为什么它不正确？

Answer 1

"The question is WHY is it incorrect?"

c++ language specification的第5.3.4章, 非常清楚地表明紧跟在 new 关键字之后的括号是为 placement new 表达式保留的: