为什么未声明NULL？
当我尝试编译以下代码时，我对此结构构造器有疑问： typedef struct Node { Node( int data ) // { this->data = data; previous = NULL; // Compiler indicates here next = NULL; } int data; Node* previous; Node* next; } NODE; 当我来这个错误发生： \linkedlist\linkedlist.h||In constructor `Node::Node(int)':| \linkedlist\linkedlist.h|9|error: `NULL' was not declared in this scope| ||=== Build finished: 1 errors, …