未定义对静态成员中的类静态成员的引用 [英] Undefined Reference to class static member in static member

问题描述

我在C ++中创建一个自引用类的链表，我想有一个名为startPointer的类型Item（Item是类名）的静态指针，所以当我调用我的静态成员函数free ，它可以通过使用Item :: startPointer释放内存，但我得到一个错误（显示在代码后）。 Pls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;
        }
    }

};

---

---

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

您必须像下面这样定义静态成员：

You have to define your static member like this:

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

在单个编译单元文件），否则刚才声明的成员。

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

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