c++ - 链接器错误(lnk2005、lnk1169)

Question

当我尝试编译时遇到这些错误:

我非常努力地尝试解决所有错误，但那三个错误获胜了。我尝试了4个小时，因为我是初学者。我非常感谢你们的帮助。

1)

Error 1 error LNK2005: "class std::basic_istream > & __cdecl cs52::operator>>(class std::basic_istream > &,class cs52::SwimmingPool &)" (??5cs52@@YAAAV?$basic_istream@DU?$char_traits@D@std@@@std@@AAV12@AAVSwimmingPool@0@@Z) already defined in POOL.obj

2)

Error 2 error LNK2005: "class std::basic_ostream > & __cdecl cs52::operator<<(class std::basic_ostream > &,class cs52::SwimmingPool const &)" (??6cs52@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV12@ABVSwimmingPool@0@@Z) already defined in POOL.obj

3)

Error 3 error LNK1169: one or more multiply defined symbols found

这是我的代码:

1)标题

#ifndef POOL_H
#define POOL_H
#include<iostream>


namespace cs52
{
    class SwimmingPool{



    public:
        SwimmingPool(int size);
        void fill(int amount);
        void splash();
        void swim();
        void evaporate(int amount);
        int getSize();
        int getContents();
        void setSize(int size);


    private:
        int mySize; // in gallons
        int myContents; // in gallons

        friend std::ostream& operator<<(std::ostream& outs, const SwimmingPool & pool);
        friend std::istream& operator>>(std::istream& ins, SwimmingPool & pool);
        friend SwimmingPool operator +(SwimmingPool& d, SwimmingPool& d2);
        friend SwimmingPool operator -(SwimmingPool& d, SwimmingPool& d2);

    };
    bool operator >(SwimmingPool& d, SwimmingPool& d2);
    bool operator <(SwimmingPool& d, SwimmingPool& d2);
    bool operator ==(SwimmingPool& d, SwimmingPool& d2);
    bool operator !=(SwimmingPool& d, SwimmingPool& d2);

    std::ostream& operator<<(std::ostream& outs, const SwimmingPool & pool){

        outs << "size " << pool.mySize << " contents " << pool.myContents;

        return outs;
    }
    std::istream& operator>> (std::istream& ins, SwimmingPool & pool)

    {
        std::cout << "enter size of pool\n";
        ins >> pool.mySize;
        pool.myContents = 0;
        return ins;
    }

}
#endif

2)这是我的第一个cpp文件

#include "POOL.h"
using namespace std;
using namespace cs52;
SwimmingPool::SwimmingPool(int size)
    {
        mySize = size;
        myContents = 0;
    }


void SwimmingPool::fill(int amount)
    {
        myContents += amount;

    }

    void SwimmingPool::splash()
    {
        cout << "splash" << std::endl;
    }


    void SwimmingPool::evaporate(int amount)
    {
        myContents -= amount;
    }


    int SwimmingPool::getSize()
    {
        return mySize;
    }


    int SwimmingPool::getContents()
    {
        return myContents;
    }

    void SwimmingPool::swim()
    {
        cout << "swimming\n";
    }
    bool cs52::operator >(SwimmingPool& d, SwimmingPool& d2)
    {
        if (d2.getSize() <d.getSize())
        {
            return true;
        }
        return false;
    }
    bool cs52::operator <(SwimmingPool& d, SwimmingPool& d2)
    {
        if (d2.getSize() >d.getSize())
        {
            return true;
        }
        return false;
    }
    bool cs52::operator ==(SwimmingPool& d, SwimmingPool& d2)
    {
        if (d2.getSize() == d.getSize())
        {
            return true;
        }

        return false;
    }
    bool cs52::operator !=(SwimmingPool& d, SwimmingPool& d2)
    {
        if (d2.getSize() != d.getSize())
        {
            return true;
        }

        return false;
    }

    SwimmingPool cs52::operator +(SwimmingPool& d, SwimmingPool& d2)
    {
        SwimmingPool s(d.getSize() + d2.getSize());
        s.fill(d.getContents() + d2.getContents());
        return s;
    }
    SwimmingPool cs52::operator -(SwimmingPool& d, SwimmingPool& d2)
    {
        if (d.getSize() >= d2.getSize() && d.getSize() >= d2.getSize())
        {
            SwimmingPool s(d.getSize() - d2.getSize());
            s.fill(d.getContents() - d2.getContents());
            return s;
        }
        else
            cout << "ERROR\n";
        return 0;
    }

3) 这是我的主 cpp 文件

#include "POOL.h"
#include<iostream>

using namespace std;
using namespace cs52;
int main()
{
    SwimmingPool smallOne(1);
    SwimmingPool bigOne(1000);
    bigOne.fill(100);
    SwimmingPool yours(10);
    yours.fill(1);
    SwimmingPool mine(20);
    mine.fill(19);


    cout << "--some tests follow--" << endl;
    SwimmingPool pool1 = mine + mine;
    SwimmingPool pool2 = yours - yours;
    if (pool1 > pool2) {
        cout << "> is working..." << endl;
    }
    if (pool1 != pool2) {
        cout << "!= is working..." << endl;
    }
    if (pool2 < pool1) {
        cout << "< is working..." << endl;
    }
    if (pool1 == pool1) {
        cout << "== is working..." << endl;
    }
    cout << "---printing pool1---" << endl;
    cout << pool1 << endl;
    cout << "---printing pool2---" << endl;
    cout << pool2 << endl;
    cout << "---reading pool1---" << endl;
    cin >> pool1;
    cout << "---printing a revised pool1---" << endl;
    cout << pool1 << endl;
    cout << "---some broken code follows---" << endl;;
    SwimmingPool badPool = smallOne - bigOne;
    system("pause");
    return 0;
}

提前致谢，

Answer 1

你定义你operator <<和operator >>头文件中的自由函数。这会导致实现被编译到两个目标文件中，从而导致重复的定义。

您必须:

1. 将它们声明为 inline
2. 将实现移至 CPP 文件中
3. 使重载方法成为类的成员，并直接在类定义主体中实现它们(这实际上使它们成为 inline )

选项 1 导致编译器不定义该函数，而是将其实现复制到调用它的任何地方。当它是编译到 DLL 中的 API 的一部分时，这可能会导致问题。交换 DLL 时，函数的更改不会影响现有程序，因为实现位于主工件中(二进制兼容性被破坏)

我认为选项 2 是最好的选择，因为它将运算符实现绑定(bind)到类实现

选项 3 在您的情况下不起作用，因为您的类必须是运算符的 LHS(运算符重载方法将在您的类的对象上调用)。输入/提取运算符的情况并非如此。