在C++中定义头文件

Question

首先，我将提到我主要来自Java背景。我确实接触过C，并且理解了C++背后的大多数概念。我试图帮助自己更多地了解这门语言，但似乎找不出标题。我理解为什么要在cpp文件和所有这些文件之外使用它们。我的问题是设法和他们一起工作。例如，使用私有浮动变量定义Vector3头，然后进行重载操作。当我试图在cpp文件中定义构造函数和方法时，我的问题就出现了。如果不明确定义头文件中的函数和构造函数，我似乎无法理解如何访问私有变量，这或多或少使我相信在这种情况下我不需要头文件和cpp文件。

下面是我当前如何定义头文件(它可以工作，但不应该是未定义的)：

#pragma once

#ifndef __Vector_3_H__
#define __Vector_3_H__

namespace VectorMath {

class Vector3 {

public:

    Vector3(float x, float y, float z) {
        this->x = x;
        this->y = y;
        this->z = z;
    }

    Vector3 operator+(Vector3 vector) {
        return Vector3(x + vector.x, y + vector.y, z + vector.z);
    }

    Vector3 operator-(Vector3 vector) {
        return Vector3(x - vector.x, y - vector.y, z - vector.z);
    }

    Vector3 operator*(Vector3 vector) {
        return Vector3(x * vector.x, y * vector.y, z * vector.z);
    }

    Vector3 operator/(Vector3 vector) {
        return Vector3(x / vector.x, y / vector.y, z / vector.z);
    }

    float getX() {
        return x;
    }

    float getY() {
        return y;
    }

    float getZ() {
        return z;
    }

private:

    float x;
    float y;
    float z;

};
}

#endif

Answer 1

它需要看起来更像这样：

Vector_3.h：

#ifndef Vector_3_H
#define Vector_3_H

#pragma once

namespace VectorMath {

class Vector3 {

public:

    Vector3(float x, float y, float z);

    Vector3 operator+(Vector3 vector);    
    Vector3 operator-(Vector3 vector);
    Vector3 operator*(Vector3 vector);
    Vector3 operator/(Vector3 vector);

    float getX();
    float getY();
    float getZ();

private:

    float x;
    float y;
    float z;

};

}

#endif

Vector_3.cpp：

#include "Vector_3.h"

namespace VectorMath {

Vector3::Vector3(float x, float y, float z) {
    this->x = x;
    this->y = y;
    this->z = z;
}

Vector3 Vector3::operator+(Vector3 vector) {
    return Vector3(x + vector.x, y + vector.y, z + vector.z);
}

Vector3 Vector3::operator-(Vector3 vector) {
    return Vector3(x - vector.x, y - vector.y, z - vector.z);
}

Vector3 Vector3::operator*(Vector3 vector) {
    return Vector3(x * vector.x, y * vector.y, z * vector.z);
}

Vector3 Vector3::operator/(Vector3 vector) {
    return Vector3(x / vector.x, y / vector.y, z / vector.z);
}

float Vector3::getX() {
    return x;
}

float Vector3::getY() {
    return y;
}

float Vector3::getZ() {
    return z;
}

}

Answer 2

如果要为构造函数使用cpp文件，则应编写

// File Vector3.cpp
#include "Vector3.h"

namespace VectorMath {

    Vector3::Vector3 (float x, float y, float z)         
    { 
        this->x=x;
       //...
    }

如果将加法保留在相同的命名空间中，则应按如下方式实现

    Vector3 Vector3::operator+(const Vector3& v)
    { 
        return Vector3 (x+v.x,y+v.y,z+v.z);
    }
}

Answer 3

如果要将成员函数的实现从头文件移开，仍然需要在类的定义中声明。例如：

// Vector1.h
#pragma once
#ifndef VectorMath_Vector1_H
#define VectorMath_Vector1_H


namespace VectorMath {

class Vector1 {

public: // Methods:

    // This is a definition for a default constructor:
    Vector1() noexcept : m_x(0) {}

    // This is a declaration for another constructor:
    Vector1(float x) noexcept;

    // This is a declaration of a member function:
    Vector1 operator+(Vector1 const & rhs) const noexcept;

private: // Fields:

    float m_x;

}; // class Vector1

} // namespace VectorMath {

#endif // VectorMath_Vector1_H

// Vector1.cpp
#include "Vector1.h"


namespace VectorMath {

// Definition of the other constructor:
Vector1::Vector1(float x) noexcept
    : m_x(x)
{}

// Definition of the binary + operator:
Vector1 Vector1::operator+(Vector1 const & rhs) const noexcept
{ return m_x + rhs.m_x; }

} // namespace VectorMath {