静态成员中对类静态成员的未定义引用

Undefined Reference to class static member in static member(静态成员中对类静态成员的未定义引用)

问题描述

我在 C++ 中创建了一个带有自引用类的链表，我想要一个名为startPointer"的类型为 Item(Item 是类名)的静态指针，以便当我调用我的静态成员函数free"时，它可以通过使用 Item::startPointer 释放内存，但我收到一个错误(在代码后显示).请帮助，

I am creating a linked list with self referential class in C++ and I want to have a static pointer of the type Item (Item is the class name) named "startPointer" so that when i call my static member function "free" , it can free up the memory by using Item::startPointer but i am getting an error(shown after code). Pls Help,

class Item
{
    public:
    std::string name;
    int row,column;
    int fileType;
    Item *ptr;
    static Item *startPointer;
    void setNextPointer(Item* ptr)
    {
        ptr=ptr;
    }
    Item *getNextPointer()
    {
        return ptr;
    }
    static void free()
        {
        Item *p,*temp;
        p=startPointer;
        while(p!=NULL)
        {
            temp=p;
            p=p->getNextPointer();
            delete temp;
        }
    }

};

<小时>

cube.o:cube.cpp:(.text$_ZN4Item4freeEv[Item::free()]+0x8): undefined reference to `Item::startPointer'
collect2: ld returned 1 exit status

mingw32-make.exe: *** [cube.exe] Error 1

Execution terminated

推荐答案

你必须像这样定义你的静态成员:

You have to define your static member like this:

Item* Item::startPointer = nullptr; // or = NULL; if your cpp version is below c++11

在单个编译单元(cpp文件)中写这样一行，否则只是声明成员.

Write such a line in a single compilation unit (cpp file), otherwise the member is just declared.

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