使用静态变量和函数的C ++类中的问题 [英] Problem in C++ class with static variables and functions

问题描述

有人可以告诉我下面的类是什么问题，g ++在ubuntu上给出错误：

 
 class FibonacciGenerator 
 {
 private：
 static int num1，num2，counting; 
 
 public：
 
 static void Reset（）
 {
 num1 = 0; num2 = 1; 
 counting = 1; 
} 
 
 static int GetCount（）
 {
 return counting; 
} 
 
 static int GetNext（）
 {
 int val = 0; 
 if（counting == 1）val = num1; 
 else if（counting == 2）val = num2; 
 else 
 {
 val = num1 + num2; 
 num1 = num2; 
 num2 = val; 
} 
 counting ++; 
 
 return val; 
} 
}; 
 

解决方案

语句 static int num1，num2，counting; code>在类定义中没有定义这些变量，它只声明它们。

一个完整的例子如下：

  //开始FibonacciGenerator.hpp 
 #ifndef FIBONACCI_GENERATOR_HPP 
 #define FIBONACCI_GENERATOR_HPP 
 class FibonacciGenerator 
 {
 private：
 static int num1，num2，counting; 
 
 public：
 / *如上* / 
}; 
 #endif // FIBONACCI_GENERATOR_HPP 
 //结束FibonacciGenerator.hpp 
 
 //开始FibonacciGenerator.cpp 
 #includeFibonacciGenerator.h
 int FibonacciGenerator :: num1; 
 int FibonacciGenerator :: num2; 
 int FibonacciGenerator :: counting; 
 //结束FibonacciGenerator.cpp 
  

如果在命名空间中声明了FibonacciGenerator，成员定义也必须在该命名空间中。

使用这样的静态成员可能是一个很糟糕的主意。最好将它们作为实例变量，这样你可以在代码的不同部分有多个独立的 FibonacciGenerators 。

Can someone tell me what is problem in the following class, g++ is giving errors on ubuntu:

class FibonacciGenerator
{
    private:
        static int num1, num2, counting;

    public:

        static void Reset()
        {
            num1 = 0; num2 = 1;
            counting = 1;
        }

        static int GetCount()
        {
            return counting;
        }

        static int GetNext()
        {
            int val = 0;
            if(counting == 1) val = num1;
            else if(counting == 2) val = num2;
            else 
            {
                val = num1 + num2;
                num1 = num2;
                num2 = val;
            }
            counting ++;

            return val;
        }
};

解决方案

The statement static int num1, num2, counting; in a class definition does not define those variables, it only declares them. If they are used they must also be defined.

A complete example of this is as follows:

//Begin FibonacciGenerator.hpp
#ifndef FIBONACCI_GENERATOR_HPP
#define FIBONACCI_GENERATOR_HPP
class FibonacciGenerator
{
private:
    static int num1, num2, counting;

public:
/* as above */
};
#endif //FIBONACCI_GENERATOR_HPP
//End FibonacciGenerator.hpp

//Begin FibonacciGenerator.cpp
#include "FibonacciGenerator.h"
int FibonacciGenerator::num1;
int FibonacciGenerator::num2;
int FibonacciGenerator::counting;
//End FibonacciGenerator.cpp

If FibonacciGenerator is declared in a namespace, then these static member definitions must also be in that namespace.

Using static members like this is probably a very bad idea. It would be better to make them instance variables, so that you could have multiple independent FibonacciGenerators in separate parts of the code.

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