c++ - 使用 .h 文件中定义的 C++ 类

Question

我在 .h 文件中实现了一个类。我正在尝试将 .h 文件导入到我的 main.cpp 中，然后在那里创建和使用该类的对象。但是，我从 Xcode 的 latex 版本中收到此错误:

ld: 1 duplicate symbol for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

这是我的代码:

类.h:

using namespace std;

class Cents
{
private:
    int m_nCents;

public:
    Cents(int nCents) { m_nCents = nCents; }

    // Add Cents + Cents
    friend Cents operator+(const Cents &c1, const Cents &c2);

    int GetCents() { return m_nCents; }
};

// note: this function is not a member function!
Cents operator+(const Cents &c1, const Cents &c2)
{
    // use the Cents constructor and operator+(int, int)
    return Cents(c1.m_nCents + c2.m_nCents);
}

这是我的 main.cpp:

    Cents cCents1(6);
    Cents cCents2(8);
    Cents cCentsSum = cCents1 + cCents2;
    cout << "I have " << cCentsSum .GetCents() << " cents." << endl;

    return 0;

帮忙吗？

编辑:这里是完整的错误信息。

duplicate symbol __ZplRK5CentsS1_ in:
    /Users/chasemccoy/Library/Developer/Xcode/DerivedData/Testing_C++-coximuwgddopngcjrkbjugfliqkv/Build/Intermediates/Testing C++.build/Debug/Testing C++.build/Objects-normal/x86_64/operatorOverload.o
    /Users/chasemccoy/Library/Developer/Xcode/DerivedData/Testing_C++-coximuwgddopngcjrkbjugfliqkv/Build/Intermediates/Testing C++.build/Debug/Testing C++.build/Objects-normal/x86_64/main.o
ld: 1 duplicate symbol for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

尝试使用预处理器指令隔离您的 header ，并且永远不要在 header 中定义实现:

#ifndef CENTS_HPP
#define CENTS_HPP

using namespace std;

class Cents
{
private:
    int m_nCents;

public:
    Cents(int nCents) { m_nCents = nCents; }

    // Add Cents + Cents
    friend Cents operator+(const Cents &c1, const Cents &c2);

    int GetCents() { return m_nCents; }
};

// note: this function is not a member function!
Cents operator+(const Cents &c1, const Cents &c2);

/* 在 cpp 中执行此操作或将其内联。

{
    // use the Cents constructor and operator+(int, int)
    return Cents(c1.m_nCents + c2.m_nCents);
} */

#endif  // CENTS_HPP