c++ - C++ 模板的编译器错误表明这不是结构体的成员

Question

我是 C++ 模板的新手，我在模板编译方面遇到了麻烦。 我想用模板编写一个类似的工厂方法，但编译器错误说'ip is not the member of _FileWriterInfo'。我很困惑，因为它已在 NetWriterInfo 结构中定义，但在 FileWriterInfo 中没有定义。如果我取消“ip”成员定义，编译器就会工作。显然 NetWriter 的 T 参数可能会错误地推断出 FileWriterInfo 结构。我怎样才能摆脱它？请帮忙。

#include <iostream>
#include <string>

enum WriterFormat
{
    WTYPE_FILE = 0,
    WTYPE_NET = 1
};

typedef struct _FileWriterInfo
{
    std::string name;
    std::string page;
}FileWriterInfo;

typedef struct _NetWriterInfo
{
    std::string name;
    std::string ip;
}NetWriterInfo;

template<typename T>
class Writer
{
public:
    virtual ~Writer() {}
    virtual std::string Write(T info) = 0;
};

template<typename T>
class FileWriter : public Writer<T>
{
public:
    std::string Write(T info) override {
        std::cout << "name:" << info.name << "\n";
        std::cout << "page:" << info.page << "\n";
        return info.name;
    }
};

template<typename T>
class NetWriter : public Writer<T>
{
public:
    std::string Write(T info) override {
        std::cout << "name:" << info.name << "\n";
        std::cout << "ip:" << info.ip << "\n";
        return info.name;
    }
};

class Creator
{
    Creator() {};
public:
    template<typename T>
    static Writer<T>* CreateWriter(WriterFormat fmt)
    {
        Writer<T>* p = nullptr;
        if (fmt == WTYPE_FILE)
            p = new FileWriter<T>;
        if (fmt == WTYPE_NET)
            p = new NetWriter<T>;
        return p;
    }
};

void WriteFile()
{
    FileWriterInfo info = { "Hello","100" };
    Writer<FileWriterInfo>* w = Creator::CreateWriter<FileWriterInfo>(WTYPE_FILE);
    w->Write(info);
    return;
}

int main()
{
    WriteFile();
    return 0;
}

Answer 1

CreateWriter 函数使用 FileWriterInfo 结构实例化 FileWriter 和 NetWriter 类。因此，编译器尝试使用 FileWriterInfo 类型实例化 NetWriter::Write 函数，但我们收到错误。

您可以将Write方法直接放置到FileWriterInfo和NetWriterInfo结构中(根据数据封装的原理)。它还可以简化代码。