c++ - 找不到 C++ 类中的静态 vector

Question

链接以下代码失败:

#include <iostream>
#include <vector>

using namespace std;
class Node {
    static vector<Node*> nodeList;
    int id;
    int value;

  public:
    Node(int);
};

Node::Node(int val) {
    id = nodeList.size();
    value = val;
    nodeList.push_back(this);
}

我收到如下错误信息。

Undefined symbols for architecture x86_64: "Node::nodeList", referenced from: Node::Node(int) in test-028e68.o "_main", referenced from: implicit entry/start for main executable ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation)

问题出现在静态 vector 上。构造函数似乎找不到符号 nodeList。我不知道如何初始化它以使代码工作。

Answer 1

你必须明白声明和定义的区别:

static vector<Node*> nodeList; // declare static member

vector<Node*> Node::nodeList; // define static member

类似于下面的内容:

class Node {...
   Node(int); // here is you declare 
};

Node::Node() {} // here is you define