C ++静态变量和未解析的外部错误 [英] C++ Static variable and unresolved externals error

问题描述

我希望我能对类的静态变量有一些澄清。

例如：
我有两个不同的类，它们执行完全不同的函数alpha和beta。在alpha内，我声明一个类型为beta的静态变量，如下所示：

  // alpha.h 
 
 #pragma once 
 #include< iostream> 
 #includebeta.h
 
 class alpha {
 public：
 alpha（）{
 
} 
 
 static beta var; 
 
 void func（）{
 var.setX（3）; 
} 
 
 void output（）{
 
} 
}; 
 
 //beta.h 
 
 #pragma once 
 #include< iostream> 
 using namespace std; 
 
 class beta {
 
 public：
 
 int x; 
 char y; 
 
 beta（）{
 x = 0; 
 y =''; 
} 
 
 void setX（int _X）{
 x = _X; 
} 
 
}; 
 
 //main.cpp 
 
 #include< iostream> 
 #include< iomanip> 
 #includealpha.h
 using namespace std; 
 
 int main（）{
 alpha x，y，z; 
 x.func（）; 
} 
  

现在当我尝试编译这个，我得到一个未解决的外部错误： / p>

错误LNK2001：未解析的外部符号public：static class beta
alpha :: var（？var @ alpha @@ 2Vbeta @@ A）

我不知道要更改什么或需要添加什么来使这样的工作。我想要x，y和z基本上共享相同的beta变量。我想我可以完成同样的事情，只是通过引用一个beta变量到每个他们。但我想知道是否可以做这个相同的事情使用static关键字这里，因为类的静态成员在类的任何实例中具有相同的值。除非我有那个定义错了。

解决方案

类中的静态变量必须仍然定义在某处，与方法类似：

把它放在main.cpp中：

  beta alpha :: var; 
  

I was hoping I could get some clarification on static variables of a class.

For example: I have two different classes which perform completely different functions, alpha and beta. Within alpha, I declare a static variable of type beta so it looks like this:

//alpha.h

#pragma once
#include <iostream>
#include "beta.h"

class alpha{
public: 
    alpha(){

    }

    static beta var; 

    void func(){
        var.setX(3);
    }

    void output(){

    }
};

//beta.h

#pragma once
#include <iostream>
using namespace std; 

class beta{

public: 

    int x; 
    char y; 

    beta(){
        x = 0; 
        y = ' '; 
    }

    void setX(int _X){
        x = _X; 
    }

};

//main.cpp

#include <iostream>
#include <iomanip>
#include "alpha.h"
using namespace std; 

int main(){
    alpha x, y, z; 
    x.func(); 
}

Now when I try to compile this, I get an unresolved externals error:

error LNK2001: unresolved external symbol "public: static class beta alpha::var" (?var@alpha@@2Vbeta@@A)

I'm not sure what to change or what else I need to add to make something like this work. I want x, y, and z to essentially share the same beta variable. I think I can accomplish this same thing by just passing by reference one beta variable into each of them. But I want to know if it's possible to do this same thing using the static keyword here because static members of a class have the same value in any instance of a class. Unless I have that definition wrong.

解决方案

static variables inside a class must still be defined somewhere, just like methods:

Put this in main.cpp:

beta alpha::var;

这篇关于C ++静态变量和未解析的外部错误的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！