对类的静态成员的未定义引用 [英] Undefined reference to a static member of the class

问题描述

我正在从事一项家庭作业作业，除了我们的教授希望我们使用的令人讨厌的静态值之外，我几乎完成了所有工作：value

I am working on a homework assignment, and I have almost everything done except for this obnoxious static value that our professor wishes us to use: value

头文件包含：

private:
    static int value;

我们必须有一个函数计算值，如下：

And we have to have a function calculate the value, like so:

static void calculate()
{
    long a = 1L;
    int count = 0;

    while( a != 0 )
    {
        a = a << 1;
        count++;
    }

    value = count;
}

这实际上是使用位移位来计算长整数中的位数。

This is essentially calculating the number of bits in a long, using bit shifting.

但是，我收到错误未定义引用`Class1 :: value'

However, I am getting the error " undefined reference to `Class1::value'

谢谢！

更新：

我包括

int Class1::value = 0;

但是，现在我得到一个错误说：错误：int Class1 :: value is private

However, now I am getting an error saying "error: int Class1::value is private

推荐答案

cpp文件添加

int ClassName::value = 0;

这将为值分配存储。

您在类声明中实际具有的一段代码声明此变量（使编译器知道这样的变量存在）。但是，每个变量必须声明并定义 。一个定义将确保存储被放在一个这个变量，并创建一个符号，你的编译器无法找到之前。

The piece of code that you actually have in a class declaration just declares this variable (makes the compiler aware that such a variable exists). However, each variable must be declared and defined. A definition will make sure the storage is put aside for this variable and create a symbol your compiler was unable to find before.

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