C++项目开发遇到的问题-优快云博客

看下面的代码：

class configbase {
public:
    configbase(const string& name, const string& description) : m_name(name), m_description(description) {}
    virtual void configd(const string& name, const string& dec);
    virtual ~configbase();

protected:
    string m_name;
    string m_description;
};

template<class T>
class config : public configbase {
public:
    config(const string& name, const string& description) : configbase(name, description) {}

    using ptr = std::shared_ptr<config>;

    void bins(const T& val) {}

    void configd(const string& name, const string& val) override {
        m_name = name;
        m_description = val;
    }
};

int main(){
	
	return 0;
}

这段代码没有问题。
但是下面的就存在问题：

    class ConfigVarBase{
    public:
        using ptr = std::shared_ptr<ConfigVarBase>;
        // 记录信息的名字和描述
        ConfigVarBase(const std::string& name,
                    const std::string& description = "")
                    :m_name(name),
                    m_description(description)
                    {
                        // 统一转换成小写
                        std::transform(m_name.begin(),
                            m_name.end(),
                            m_name.begin(),
                            ::tolower
                        );
                    }
        virtual ~ConfigVarBase(){}
        const std::string& getName() const {return m_name;}
        const std::string& getDescription()const{return m_description;}

        virtual std::string toString();//{return "";}
        virtual bool fromString(const std::string& val);//{ return true;}
        // 拿到信息的类型名字
        virtual std::string getTypename()const;//{return "";}
        protected:
            std::string m_name;
            std::string m_description;
    };
    // 根据不同的类型进行构建信息对象
    template<class T>
    class configvar:public ConfigVarBase{
    public:
        using ptr = std::shared_ptr<configvar>;
        configvar(
        const std::string& name,
        const T& default_value,
        const std::string& descriiption="" 
        ):ConfigVarBase(name, descriiption){
            m_val = default_value;
        }
        ~configvar(){}
        // 将信息转换成字符串
        std::string toString()override{
            try
            {
                return boost::lexical_cast<std::string>(m_val);
            }
            catch(const std::exception& e)
            {
                SYLAR_LOG_ERROR(SYLAR_LOG_ROOT())<<"configvar::tostring exception"
                << e.what()<<"convert:"<<typeid(m_val).name()<<"to string";
                // std::cerr << e.what() << '\n';
            }
            return "";
        }
        // 将字符串转化成信息，并返回转化的结果
        bool fromString(const std::string& val)override{
            try
            {
                m_val = boost::lexical_cast<T>(val);
                return true;
            }
            catch(const std::exception& e)
            {
                SYLAR_LOG_ERROR(SYLAR_LOG_ROOT())<<"configvar::fromstring exception"
                <<e.what()<<"convert:string to"<<typeid(m_val).name();
            }
            return false;
        }
        T getValue()const{return m_val;}
        std::string getTypename()const override{
            // 对T变成字符串
            return "";
        }
        void setValue(const T& value)const{m_val = value;}
        private:
            T m_val;
    };

如果说我将基类中的虚函数进行空实现，此时就没有问题。第一段代码没有做成动态库。第二个是做成了动态库的代码。
错误信息：

Undefined symbols for architecture arm64:
  "typeinfo for sylar::ConfigVarBase", referenced from:
      std::__1::shared_ptr<sylar::configvar<int> > std::__1::dynamic_pointer_cast[abi:v15006]<sylar::configvar<int>, sylar::ConfigVarBase>(std::__1::shared_ptr<sylar::ConfigVarBase> const&) in test_config.cpp.o
      typeinfo for sylar::configvar<int> in test_config.cpp.o
  "vtable for sylar::ConfigVarBase", referenced from:
      sylar::ConfigVarBase::ConfigVarBase(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) in test_config.cpp.o
      sylar::ConfigVarBase::~ConfigVarBase() in test_config.cpp.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [/Users/al/Desktop/C++/workspace/bin/test_config] Error 1
make[1]: *** [CMakeFiles/test_config.dir/all] Error 2
make: *** [all] Error 2