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Dzious's questions

Martin Hope
Dzious
Asked: 2024-10-02 07:13:54 +0800 CST
  • 8

我std::unordered_set第一次使用自定义类型，我不知道我缺少什么来编译contains()我的集合。

我基本上有一个看起来像这样的课程：

class MyClass
{
// Ctor/Dtor
public:
    MyClass(const std::string& name /* + other params in my real use case */) : m_name(name) {}
    ~MyClass() = default;

// Members
private:
    std::string m_name;

// Operators
public:
    // Equal operators
    bool operator==(const MyClass &other) const
    {
        return m_name == other.m_name;
    }

    bool operator==(const std::string& other) const
    {
        return m_name == other;
    }

    bool operator==(const char* other) const
    {
        return m_name == other;
    }

// Functors
public:
    // Hash functor
    struct Hash
    {
        std::size_t operator()(const MyClass &class_) const
        {
            return std::hash<std::string>()(class_.m_name);
        }

        std::size_t operator()(const std::string &name) const
        {
            return std::hash<std::string>()(name);
        }

        std::size_t operator()(const char* name) const 
        {
            return std::hash<std::string>()(name);
        }
    };

    // Equal functor
    struct Equal
    {
        bool operator()(const MyClass &lhs, const MyClass &rhs) const
        {
            return lhs.m_name == rhs.m_name;
        }

        bool operator()(const MyClass &lhs, const std::string &rhs) const
        {
            return lhs.m_name == rhs;
        }

        bool operator()(const std::string &lhs, const MyClass &rhs) const
        {
            return lhs == rhs.m_name;
        }

        bool operator()(const MyClass &lhs, const char* rhs) const
        {
            return lhs.m_name == rhs;
        }

        bool operator()(const char* lhs, const MyClass &rhs) const
        {
            return lhs == rhs.m_name;
        }
    };

};

使用此类，我想创建一个std::unordered_set并检查名称为的元素是否key1存在。为此，我想使用以下代码：

int main()
{
    // I tried both, but none of them seem to work
    std::unordered_set<MyClass, MyClass::Hash, MyClass::Equal> set;
    // std::unordered_set<MyClass, MyClass::Hash> set;

    // Add sample elements to the set
    set.emplace("key1");
    set.emplace("key2");

    // Check if the set contains "key1"
    if (set.contains("key1")) // Compile error on this line. Why does this not work?
    {
        std::wcout << L"set contains key1." << std::endl;
    } else {
        std::wcout << L"set doesn't contain key1." << std::endl;
    }

    return 0;
}

但是我在调​​用时不断收到编译器错误contains()：

错误：没有匹配的函数来调用‘std::unordered_set<MyClass, MyClass::Hash, MyClass::Equal>::contains(const char [5])’[...]

我不知道为什么，也找不到任何有关它的资源。

我想我遗漏了一些东西，因为下面的代码使用起来没有问题std::string：

int main()
{
    std::unordered_set<std::string> set;
   
    // Add sample elements to the set
    set.emplace("key1");
    set.emplace("key2");

    // Check if the set contains "key1"
    if (set.contains("key1")) // Why does this not work?
    {
        std::wcout << L"set contains key1." << std::endl;
    } else {
        std::wcout << L"set doesn't contain key1." << std::endl;
    }

    return 0;
}
c++