我得到一个“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:

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);
    };
}

和.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;
    }
}

好，所以在构造函数中我没有问题，但是在 getPoint()函数中，我得到非静态成员引用必须相对于特定对象"错误，并且不会让我使用变量.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.我该怎么做才能解决此问题?

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?

推荐答案

它不会让我使用变量

it won't let me use the variables

您无法从 Point :: getPoint访问 X ， Y ， Z 和 alpha ，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 static 类成员.

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.

我尝试将变量设为静态，但这给了我无法解决的外部符号错误

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

仅通过添加 static 关键字就无法使成员成为静态成员，还需要定义它们(例如， double Point :: X; ).

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

该如何解决?

将 getPoint 函数设为非静态，并将其更新为使用引用.

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;
}

如果您不使用参数引用，则函数完成后更改将丢失，因为参数是按值传递的(即，它们是原始副本)，这将修改仅存在于范围内的临时变量 getPoint 函数的功能.

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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