我得到“非静态成员引用必须相对于特定对象”。 DLL项目C ++中的错误 [英] I get a "nonstatic member reference must be relative to specific object" error in a DLL project C++

问题描述

我正在处理一个DLL项目，正在编写一个类，其标题中包含变量和函数，并在.cpp文件中定义如下：

.h：

  #ifndef RE_MATH_H 
 #define RE_MATH_H 
 #ifdef MATHFUNCSDLL_EXPORTS 
＃定义RE_MATH_API __declspec（dllimport）
 #else 
＃定义RE_MATH_API __declspec（dllexport）
 #endif 
＃定义PI 3.14159265358979323846 
 
命名空间RE_Math 
 {
类RE_MATH_API点
 {
 public：
 double X; 
双倍Y； 
 double Z; 
 float alpha; 
 
 Point（double x，double y，double z，float a）; 
 static void getPoint（double x，double y，double z，float a）; 
}; 
} 
  

和.cpp：

  #include< re_math.h> 
 
命名空间RE_Math 
 {
 Point :: Point（double x，double y，double z，float a）
 {
 X = x; 
 Y = y; 
 Z = z; 
 alpha = a; 
} 
 
 void Point :: getPoint（double x，double y，double z，float a）
 {
 x = X; 
 y = Y; 
 z = Z; 
 a = alpha; 
} 
} 
  

好的，所以在构造函数中我没有问题，但是在 getPoint（）函数中，出现非静态成员引用必须相对于特定对象错误，并且它不允许我使用变量。我尝试将变量设为静态，但这在getPoint（）中的相同位置给了我未解决的外部符号错误。
我应该怎么做才能解决此问题？

解决方案

它不会让我使用变量

您无法访问 X ， Y ， Z 和 alpha 从 Point :: getPoint ，因为 getPoint 函数是静态的。静态成员函数无法访问实例数据成员，但可以访问静态类成员。

我尝试将变量设为静态，但这使我无法解决外部符号错误

您不能通过简单地添加静态关键字，还需要定义它们（例如， double Point :: X; ）。

我该怎么解决？

将 getPoint 函数设为非静态，并对其进行更新以使用引用。

  void Point :: getPoint（double& x，double& y，double& z，float& a）
 {
x = X; 
 y = Y; 
 z = Z; 
 a = alpha; 
} 
  

如果不使用引用作为参数，则在该函数完成是因为参数是按值传递的（即，它们是原始副本），该值正在修改仅在 getPoint 函数范围内存在的临时变量。 / p>

I'm working on a DLL project, I'm writing a class with variables and functions in a header and the definitions in a .cpp file like this:

.h:

#ifndef RE_MATH_H
#define RE_MATH_H
#ifdef MATHFUNCSDLL_EXPORTS
#define RE_MATH_API __declspec(dllimport) 
#else
#define RE_MATH_API __declspec(dllexport) 
#endif
#define PI 3.14159265358979323846

namespace RE_Math
{
    class RE_MATH_API Point
    {
        public:
            double X;
            double Y;
            double Z;
            float alpha;

            Point(double x, double y, double z, float a);
            static void getPoint(double x, double y, double z, float a);
    };
}

and the .cpp:

#include <re_math.h>

namespace RE_Math
{
    Point::Point(double x, double y, double z, float a)
    {
        X = x;
        Y = y;
        Z = z;
        alpha = a;
    }

    void Point::getPoint(double x, double y, double z, float a)
    {
        x = X;
        y = Y;
        z = Z;
        a = alpha;
    }
}

OK, so in the constructor I have no problems, but in the getPoint() function I get the "non-static member reference must be relative to specific object" error and it won't let me use the variables. I tried making the variables static, but that gives me unresolved external symbol errors in the same places, in getPoint(). What should I do to fix this?

解决方案

it won't let me use the variables

You cannot access X, Y, Z, and alpha from Point::getPoint because the getPoint function is static. A static member function cannot access instance data members but it can access static class members.

I tried making the variables static, but that gives me unresolved external symbol errors

You cannot make the members static by simply adding the static keyword, you need to define them as well (e.g., double Point::X;).

What should I do to fix this?

Make the getPoint function non-static and updated it to use references.

void Point::getPoint(double& x, double& y, double& z, float& a)
{
    x = X;
    y = Y;
    z = Z;
    a = alpha;
}

If you don't use references for the parameters the changes are lost after the function completes because the parameters are passed by-value (i.e., they are copies of the originals) which is modifying temporary variables that only exist within the scope of the getPoint function.

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