C++ 实现Variant类

缺乏、安全感 2021-11-29 10:40 259阅读 0赞

Variant类借鉴于Qt的QVariant类，类似于Boost的any类。它把常用类型使用一个类包装起来，这样使用QVector等容器时，其内部就可以存储不同的数据。例如：

std::vector<Variant> vec;
    vec.push_back(1);        // 整形
    vec.push_back("str");    // 字符串
    vec.push_back(false);    // bool变量
    vec.push_back(1.2);      // 浮点数

当然，没有做到像QVariant类那么全面，现阶段仅仅提供了基本数据类型和std::string、std::wstring、char \*, wchar\_t \*类型的数据封装。后续若有完善，再另行给出源码，目前版本仅仅为大家提供一个参考，与大家共同学习与交流。话不多说，上源码：

（编译器：VS2017 msvc15）

/**
     * \filename    Variant.h
     * \breif        The header file of class Variant.
     * \date        2019-07-21
     * \author        shaoguang
     */
    
    #ifndef VARIANT_H
    #define VARIANT_H
    
    #include <string>
    
    class Variant
    {
    public:
        using uchar = unsigned char;
        using ushort = unsigned short;
        using uint = unsigned int;
        using ulong = unsigned long;
        using ulonglong = unsigned long long;
        using wchar = wchar_t;
    public:
        enum Type {
            Invalid,
            Bool,
            Char,
            UChar,
            Short,
            UShort,
            Int,
            UInt,
            Long,
            ULong,
            LongLong,
            ULongLong,
            Float,
            Double,
            LongDouble,
            WChar,
    
            String,            // std::string
            WString,        // std::wstring
        };
    
        template<typename T>
        static Type typeID();
    public:
        Variant();
        ~Variant();
    
        Variant(bool b);
        Variant(char c);
        Variant(uchar uc);
        Variant(wchar_t wc);
        Variant(short s);
        Variant(ushort us);
        Variant(int i);
        Variant(uint ui);
        Variant(long l);
        Variant(ulong ul);
        Variant(long long ll);
        Variant(ulonglong ull);
        Variant(float f);
        Variant(double d);
        Variant(long double ld);
        Variant(const char *str);
        Variant(const wchar_t *wstr);
        Variant(const std::string &str);
        Variant(const std::wstring &wstr);
    
        Variant(const Variant &other);
        Variant(Variant &&other);
        Variant &operator=(const Variant &other);
        Variant &operator=(Variant &&other);
    
        Type type() const;
        bool canConvert(Type type) const;
        bool isValid() const;
    
        bool toBool() const;
        char toChar() const;
        uchar toUchar() const;
        wchar toWChar() const;
        short toShort() const;
        ushort toUShort() const;
        int toInt() const;
        uint toUInt() const;
        long toLong() const;
        ulong toULong() const;
        long long toLongLong() const;
        ulonglong toULongLong() const;
        float toFloat() const;
        double toDouble() const;
        long double toLongDouble() const;
        std::string toString() const;
        std::wstring toWString() const;
    
    
    private:
        void make_invalid();
    
        template<typename T>
        static T strToNumber(const std::string &str);
        template<typename T>
        static T strToNumber(const std::wstring &wstr);
    
        template<typename T>
        T numVariantToHelper(const T &val) const;
    
        template <typename T>
        static inline void safe_delete_void_ptr(void *&target);
    
    private:
        struct Private {
            inline Private() noexcept : type(Invalid), is_shared(false), is_null(true)
            {
                data.ptr = nullptr;
            }
    
            // Internal constructor for initializing variant.
            explicit inline Private(Type variantType) noexcept
                : type(variantType), is_shared(false), is_null(false)
            {}
    
            inline Private(const Private &other) noexcept
                : data(other.data), type(other.type),
                is_shared(other.is_shared), is_null(other.is_null)
            {}
    
            union Data {
                bool b;
                char c;
                uchar uc;
                wchar_t wc;
                short s;
                ushort us;
                int i;
                uint ui;
                long l;
                ulong ul;
                long long ll;
                ulonglong ull;
                float f;
                double d;
                long double ld;
                void *ptr;
            }data;
    
            Type type;
            bool is_shared;
            bool is_null;
        };
        Private        _d;
    };
    
    #endif    // VARIANT_H

#include "Variant.h"
    
    #include <sstream>
    
    Variant::Variant()
        : _d(Invalid)
    {
    }
    
    Variant::~Variant()
    {
        if (String == _d.type)
        {
            if (_d.data.ptr)
                safe_delete_void_ptr<char *>(_d.data.ptr);
        }
        else if (WString == _d.type)
        {
            if (_d.data.ptr)
                safe_delete_void_ptr<wchar_t *>(_d.data.ptr);
        }
    }
    
    Variant::Variant(bool b)
        : _d(Bool)
    {
        _d.data.b = b;
    }
    
    Variant::Variant(char c)
        : _d(Char)
    {
        _d.data.c = c;
    }
    
    Variant::Variant(uchar uc)
        : _d(UChar)
    {
        _d.data.uc = uc;
    }
    
    Variant::Variant(wchar_t wc)
        : _d(WChar)
    {
        _d.data.wc = wc;
    }
    
    Variant::Variant(short s)
        : _d(Short)
    {
        _d.data.s = s;
    }
    Variant::Variant(ushort us)
        : _d(UShort)
    {
        _d.data.us = us;
    }
    Variant::Variant(int i)
        : _d(Int)
    {
        _d.data.i = i;
    }
    Variant::Variant(uint ui)
        : _d(UInt)
    {
        _d.data.ui = ui;
    }
    Variant::Variant(long l)
        : _d(Long)
    {
        _d.data.l = l;
    }
    Variant::Variant(ulong ul)
        : _d(ULong)
    {
        _d.data.ul = ul;
    }
    Variant::Variant(long long ll)
        : _d(LongLong)
    {
        _d.data.ll = ll;
    }
    Variant::Variant(ulonglong ull)
        : _d(ULongLong)
    {
        _d.data.ull = ull;
    }
    Variant::Variant(float f)
        : _d(Float)
    {
        _d.data.f = f;
    }
    Variant::Variant(double d)
        : _d(Double)
    {
        _d.data.d = d;
    }
    Variant::Variant(long double ld)
        : _d(LongDouble)
    {
        _d.data.ld = ld;
    }
    
    Variant::Variant(const char *str)
        : _d(String)
    {
        if (!str) {
            make_invalid();
        } else {
            size_t len = strlen(str);
            _d.data.ptr = new char[strlen(str) + 1];
            strcpy_s(static_cast<char *>(_d.data.ptr), strlen(str) + 1, str);
        }
    }
    
    Variant::Variant(const wchar_t * wstr)
    {
        if (!wstr) {
            make_invalid();
        } else {
            _d.data.ptr = new char[wcslen(wstr) + 1];
            wcscpy_s((wchar_t *)_d.data.ptr, wcslen(wstr) + 1, wstr);
        }
    }
    
    Variant::Variant(const std::string &str)
        : _d(String)
    {
        if (str.empty()) {
            make_invalid();
        } else {
            _d.data.ptr = new char[str.size() + 1];
            strcpy_s((char *)_d.data.ptr, str.size() + 1, str.c_str());
        }
    }
    
    Variant::Variant(const std::wstring &wstr)
        : _d(WString)
    {
        if (wstr.empty()) {
            make_invalid();
        } else {
            _d.data.ptr = new wchar_t[wstr.size() + 1];
            wcscpy_s((wchar_t *)_d.data.ptr, wstr.size() + 1, wstr.c_str());
        }
    }
    
    Variant::Variant(const Variant &other)
        : _d(other._d)
    {
        if (String == _d.type)
        {
            _d.data.ptr = new char[strlen(static_cast<char *>(other._d.data.ptr)) + 1];
            strcpy_s(static_cast<char *>(_d.data.ptr), strlen(static_cast<char *>(other._d.data.ptr)) + 1,
                static_cast<char *>(other._d.data.ptr));
        }
        else if (WString == _d.type)
        {
            _d.data.ptr = new char[wcslen(static_cast<wchar_t *>(other._d.data.ptr)) + 1];
            wcscpy_s(static_cast<wchar_t *>(_d.data.ptr), wcslen(static_cast<wchar_t *>(other._d.data.ptr)) + 1,
                static_cast<wchar_t *>(other._d.data.ptr));
        }
    }
    Variant::Variant(Variant &&other)
        : _d(other._d)
    {
        if (String == other._d.type || WString == other._d.type)
        {
            this->_d.data.ptr = other._d.data.ptr;
            other.make_invalid();
        }
    }
    
    Variant &Variant::operator=(const Variant &other)
    {
        if (this == &other)
            return *this;
        if (String == _d.type || WString == _d.type)
        {
            if (_d.data.ptr)
            {
                delete []_d.data.ptr;
                _d.data.ptr = nullptr;
            }
        }
        if (Invalid == other._d.type)
        {
            make_invalid();
            return *this;
        }
        else if (String == other._d.type)
        {
            _d.data.ptr = new char[strlen(static_cast<char *>(other._d.data.ptr)) + 1];
            strcpy_s(static_cast<char *>(_d.data.ptr), strlen(static_cast<char *>(other._d.data.ptr)) + 1,
                static_cast<char *>(other._d.data.ptr));
        }
        else if (WString == other._d.type)
        {
            _d.data.ptr = new char[wcslen(static_cast<wchar_t *>(other._d.data.ptr)) + 1];
            wcscpy_s(static_cast<wchar_t *>(_d.data.ptr), wcslen(static_cast<wchar_t *>(other._d.data.ptr)) + 1,
                static_cast<wchar_t *>(other._d.data.ptr));
        }
        else
            _d.data = other._d.data;
        this->_d.type = other._d.type;
        this->_d.is_null = other._d.is_null;
        this->_d.is_shared = other._d.is_shared;
        return *this;
    }
    Variant &Variant::operator=(Variant &&other)
    {
        if (this == &other)
            return *this;
        this->_d = other._d;
        if (String == _d.type || WString == _d.type)
        {
            this->_d.data.ptr = other._d.data.ptr;
            other.make_invalid();
        }
        return *this;
    }
    
    Variant::Type Variant::type() const
    {
        return _d.type;
    }
    
    bool Variant::canConvert(Type type) const
    {
        if (Invalid == type)
            return false;
        switch (_d.type)
        {
        case Invalid:        return false;
        case Char:            return WChar != type && WString != type;
        case UChar:            return WChar != type && WString != type;
        case WChar:            return Char != type && String != type;
        case Short:            return true;
        case UShort:        return true;
        case Int:            return true;
        case UInt:            return true;
        case Long:            return true;
        case ULong:            return true;
        case LongLong:        return true;
        case ULongLong:        return true;
        case Float:            return Char != type && UChar != type && WChar != type;
        case Double:        return Char != type && UChar != type && WChar != type;
        case LongDouble:    return Char != type && UChar != type && WChar != type;
        case String:        return WString != type;
        case WString:        return String != type;
        default: break;
        }
        return false;
    }
    
    bool Variant::isValid() const
    {
        return _d.type != Invalid;
    }
    
    std::string Variant::toString() const
    {
        if (!isValid() || WString == _d.type)
            return "";
        if (String == _d.type)
            return static_cast<char *>(_d.data.ptr);
    
        std::stringstream ss;
        try {
            switch (_d.type)
            {
            case Bool:
                if (_d.data.b) ss << "true";
                else ss << "false"; break;
            case Char:            ss << _d.data.c;    break;
            case UChar:            ss << _d.data.uc;    break;
            case WChar:                                break;
            case Short:            ss << _d.data.s;    break;
            case UShort:        ss << _d.data.us;    break;
            case Int:            ss << _d.data.i;    break;
            case UInt:            ss << _d.data.ui;    break;
            case Long:            ss << _d.data.l;    break;
            case ULong:            ss << _d.data.ul;    break;
            case LongLong:        ss << _d.data.ll;    break;
            case ULongLong:        ss << _d.data.ull;    break;
            case Float:            ss << _d.data.f;    break;
            case Double:        ss << _d.data.d;    break;
            case LongDouble:    ss << _d.data.ld;    break;
            default: break;
            }
        } catch (...) {
            return ss.str();
        }
    
        return ss.str();
    }
    
    std::wstring Variant::toWString() const
    {
        if (!isValid() || String == _d.type)
            return L"";
        if (WString == _d.type)
            return static_cast<wchar_t *>(_d.data.ptr);
    
        std::wstringstream wss;
        try {
            switch (_d.type)
            {
            case Bool:
                if (_d.data.b) wss << L"true";
                else wss << L"false"; break;
            case Char:            wss << _d.data.c;    break;
            case UChar:            wss << _d.data.uc;    break;
            case WChar:            wss << _d.data.wc;    break;
            case Short:            wss << _d.data.s;    break;
            case UShort:        wss << _d.data.us;    break;
            case Int:            wss << _d.data.i;    break;
            case UInt:            wss << _d.data.ui;    break;
            case Long:            wss << _d.data.l;    break;
            case ULong:            wss << _d.data.ul;    break;
            case LongLong:        wss << _d.data.ll;    break;
            case ULongLong:        wss << _d.data.ull;    break;
            case Float:            wss << _d.data.f;    break;
            case Double:        wss << _d.data.d;    break;
            case LongDouble:    wss << _d.data.ld;    break;
            default: break;
            }
        } catch (...) {
            return wss.str();
        }
    
        return wss.str();
    }
    bool Variant::toBool() const
    {
        switch (_d.type)
        {
        case Bool:    return _d.data.b;
        case String: return (strcmp((char *)_d.data.ptr, "true") == 0);
        case WString: return (wcscmp((wchar_t *)_d.data.ptr, L"true") == 0);
        default: return numVariantToHelper<bool>(_d.data.b);
        }
    }
    char Variant::toChar() const
    {
        return numVariantToHelper<char>(_d.data.c);
    }
    Variant::uchar Variant::toUchar() const
    {
        return numVariantToHelper<uchar>(_d.data.uc);
    }
    wchar_t Variant::toWChar() const
    {
        return numVariantToHelper<wchar_t>(_d.data.wc);
    }
    short Variant::toShort() const
    {
        return numVariantToHelper<short>(_d.data.s);
    }
    Variant::ushort Variant::toUShort() const
    {
        return numVariantToHelper<ushort>(_d.data.us);
    }
    int Variant::toInt() const
    {
        return numVariantToHelper<int>(_d.data.i);
    }
    Variant::uint Variant::toUInt() const
    {
        return numVariantToHelper<uint>(_d.data.ui);
    }
    long Variant::toLong() const
    {
        return numVariantToHelper<long>(_d.data.l);
    }
    Variant::ulong Variant::toULong() const
    {
        return numVariantToHelper<ulong>(_d.data.ul);
    }
    long long Variant::toLongLong() const
    {
        return numVariantToHelper<long long>(_d.data.ll);
    }
    Variant::ulonglong Variant::toULongLong() const
    {
        return numVariantToHelper<ulonglong>(_d.data.ull);
    }
    float Variant::toFloat() const
    {
        return numVariantToHelper<float>(_d.data.f);
    }
    double Variant::toDouble() const
    {
        return numVariantToHelper<double>(_d.data.d);
    }
    long double Variant::toLongDouble() const
    {
        return numVariantToHelper<long double>(_d.data.ld);
    }
    
    void Variant::make_invalid()
    {
        _d.type = Invalid;
        _d.is_null = true;
        _d.is_shared = false;
        _d.data.ptr = nullptr;
    }
    
    template<typename T>
    Variant::Type Variant::typeID()
    {
        if (std::is_same_v<T, bool>)
            return Bool;
        if (std::is_same_v<T, char>)
            return Char;
        if (std::is_same_v<T, uchar>)
            return UChar;
        if (std::is_same_v<T, wchar_t>)
            return WChar;
        if (std::is_same_v<T, short>)
            return Short;
        if (std::is_same_v<T, ushort>)
            return UShort;
        if (std::is_same_v<T, int>)
            return Int;
        if (std::is_same_v<T, uint>)
            return UInt;
        if (std::is_same_v<T, long>)
            return Long;
        if (std::is_same_v<T, ulong>)
            return ULong;
        if (std::is_same_v<T, long long>)
            return LongLong;
        if (std::is_same_v<T, ulonglong>)
            return ULongLong;
        if (std::is_same_v<T, float>)
            return Float;
        if (std::is_same_v<T, double>)
            return Double;
        if (std::is_same_v<T, long double>)
            return LongDouble;
        if (std::is_same_v<T, std::string>)
            return String;
        if (std::is_same_v<T, std::wstring>)
            return WString;
    
        return Invalid;
    }
    
    template<typename T>
    T Variant::strToNumber(const std::string &str)
    {
        try {
            switch (typeID<T>())
            {
            case Bool:            return stoi(str);        break;
            case Char:            return stoi(str);        break;
            case UChar:            return stoul(str);        break;
            case WChar:            return stoi(str);        break;
            case Short:            return stoi(str);        break;
            case UShort:        return stoul(str);        break;
            case Int:            return stoi(str);        break;
            case UInt:            return stoul(str);        break;
            case Long:            return stol(str);        break;
            case ULong:            return stoul(str);        break;
            case LongLong:        return stoll(str);        break;
            case ULongLong:        return stoull(str);;    break;
            case Float:            return stof(str);        break;
            case Double:        return stod(str);        break;
            case LongDouble:    return stold(str);        break;
            default: break;
            }
        } catch (...) {
            return T();
        }
    
        return T();
    }
    
    template<typename T>
    T Variant::strToNumber(const std::wstring &wstr)
    {
        try {
            switch (typeID<T>())
            {
            case Bool:            return stoi(wstr);        break;
            case Char:            return stoi(wstr);        break;
            case UChar:            return stoul(wstr);        break;
            case WChar:            return stoi(wstr);        break;
            case Short:            return stoi(wstr);        break;
            case UShort:        return stoul(wstr);        break;
            case Int:            return stoi(wstr);        break;
            case UInt:            return stoul(wstr);        break;
            case Long:            return stol(wstr);        break;
            case ULong:            return stoul(wstr);        break;
            case LongLong:        return stoll(wstr);        break;
            case ULongLong:        return stoull(wstr);;    break;
            case Float:            return stof(wstr);        break;
            case Double:        return stod(wstr);        break;
            case LongDouble:    return stold(wstr);        break;
            default: break;
            }
        } catch (const std::exception&) {
            return T();
        }
    
        return T();
    }
    
    template<typename T>
    T Variant::numVariantToHelper(const T &val) const
    {
        if (typeID<T>() == _d.type)
            return val;
    
        switch (_d.type)
        {
        case Bool:            return T(_d.data.b);    break;
        case Char:            return T(_d.data.c);    break;
        case UChar:            return T(_d.data.uc);    break;
        case WChar:            return T(_d.data.wc);    break;
        case Short:            return T(_d.data.s);    break;
        case UShort:        return T(_d.data.us);    break;
        case Int:            return T(_d.data.i);    break;
        case UInt:            return T(_d.data.ui);    break;
        case Long:            return T(_d.data.l);    break;
        case ULong:            return T(_d.data.ui);    break;
        case LongLong:        return T(_d.data.ll);    break;
        case ULongLong:        return T(_d.data.ull);;    break;
        case Float:            return T(_d.data.f);    break;
        case Double:        return T(_d.data.d);    break;
        case LongDouble:    return T(_d.data.ld);    break;
        case String:        return strToNumber<T>(static_cast<char *>(_d.data.ptr));
        case WString:        return strToNumber<T>(static_cast<wchar_t *>(_d.data.ptr));
        default: break;
        }
        return T();
    }
    
    template<typename T>
    inline void Variant::safe_delete_void_ptr(void *&target)
    {
        if (target)
        {
            T temp = static_cast<T>(target);
            delete []temp;
            temp = nullptr;
            target = nullptr;
        }
    }

下面写一个简单的测试程序：

#include <iostream>
    #include <stdlib.h>
    using namespace std;
    
    #include "Variant.h"
    #include <vector>
    
    int main(int argc, char *argv[])
    {
        std::vector<Variant> vec;
        vec = {true, 'c', 1, 1.2, "shaoguang"};
    
        for (auto &v : vec)
            std::cout << v.toString() << std::endl;
    
        system("pause");
        return 0;
    }

输出结果：

![20190721223945773.png][]

[20190721223945773.png]: /images/20211129/36e91d53c1e544b984b72d22b6921f79.png