Question

我是一名C ++新手，我正在尝试使用boost序列化，我想看看当一个类被声明为另一个类的成员时它是否有效。但是当我编译我的代码时，我会遇到很多错误。我尝试将基于声明为结构，但没有更改错误。我的代码：

#include <iostream>
#include <fstream>
#include <boost/archive/text_iarchive.hpp>
#include <boost/archive/text_oarchive.hpp>

class baseds{};
class superior{};

class baseds {
private:
    friend class boost::serialization::access;
public:
    int a;
    int b;
    int c;
    baseds(){}
    ~baseds(){}
    template <class Archive>
    void serialize(Archive & ar, const unsigned int version)
    {
        ar & a;
        ar & b;
        ar & c;
    }
};

class superior  {
private:
    friend class boost::serialization::access;
public:
    int x;
    int y;
    baseds lag;
    superior(){}
    ~superior(){}
    template <class Archive>
    void serialize(Archive & ar, const unsigned int version)
    {
        ar & x;
        ar & y;
        ar & lag;
    }
};

int main()  {

    superior myData,myData2;
    myData.x=10;
    myData.y=20;
    myData.lag.a=1;
    myData.lag.b=2;
    myData.lag.c=3;

    ofstream ofs("steps.txt");
    {
        boost::serialization::archive one(ofs);
        one << myData;
    }

    ifstream ifs("steps.txt");
    {
        boost::serialization::archive two(ifs);
        two >> myData2;
    }
    std::cout<<"\n"<<myData2.x;
    std::cout<<"\n"<<myData2.y;
    std::cout<<"\n"<<myData2.lag.a;
    std::cout<<"\n"<<myData2.lag.b;
    std::cout<<"\n"<<myData2.lag.c;

    return 0;

}

错误：

tier2.cpp:10: error: a class-key must be used when declaring a friend
tier2.cpp:29: error: a class-key must be used when declaring a friend
tier2.cpp:32: error: expected `;' before "int"
tier2.cpp: In member function `void superior::serialize(Archive&, unsigned int)':
tier2.cpp:38: error: `x' undeclared (first use this function)
tier2.cpp:38: error: (Each undeclared identifier is reported only once for each function it appears in.)
tier2.cpp:39: error: `y' undeclared (first use this function)
tier2.cpp:40: error: `lag' undeclared (first use this function)
tier2.cpp: In function `int main()':
tier2.cpp:47: error: 'class superior' has no member named 'x'
tier2.cpp:48: error: 'class superior' has no member named 'y'
tier2.cpp:49: error: 'class superior' has no member named 'lag'
tier2.cpp:50: error: 'class superior' has no member named 'lag'
tier2.cpp:51: error: 'class superior' has no member named 'lag'
tier2.cpp:53: error: `ofstream' undeclared (first use this function)
tier2.cpp:53: error: expected `;' before "ofs"
tier2.cpp:55: error: `archive' is not a member of `boost::serialization'
tier2.cpp:55: error: expected `;' before "one"
tier2.cpp:56: error: `one' undeclared (first use this function)
tier2.cpp:57: error: expected `;' before '}' token
tier2.cpp:59: error: `ifstream' undeclared (first use this function)
tier2.cpp:59: error: expected `;' before "ifs"
tier2.cpp:61: error: `archive' is not a member of `boost::serialization'
tier2.cpp:61: error: expected `;' before "ones"
tier2.cpp:62: error: `ones' undeclared (first use this function)
tier2.cpp:63: error: expected `;' before '}' token
tier2.cpp:64: error: 'class superior' has no member named 'x'
tier2.cpp:65: error: 'class superior' has no member named 'y'
tier2.cpp:66: error: 'class superior' has no member named 'lag'
tier2.cpp:67: error: 'class superior' has no member named 'lag'
tier2.cpp:68: error: 'class superior' has no member named 'lag'
tier2.cpp:71:2: warning: no newline at end of file

Answer 1

您正在重新定义baseds和superior。您应该收到类似于

的错误

class baseds{};   // definition
class superior{}; // definition

// second definition
class baseds {
private:
 ....

错误：重新定义'class baseds'

删除第一对定义。

Answer 2

您要定义baseds和superior两次。

在gcc上你会得到正确的错误信息：

main.cpp:9:7: error: redefinition of 'baseds'
class baseds {
      ^
main.cpp:6:7: note: previous definition is here
class baseds{};
      ^
main.cpp:27:7: error: redefinition of 'superior'
class superior  {
      ^
main.cpp:7:7: note: previous definition is here
class superior{};

看起来您的编译器无法识别重新定义并丢失，从而产生错误的错误消息。

如果您打算提供两个类的前向声明，则需要丢失大括号：

class baseds;
class superior;

class baseds {
  /* ... */
};

但是你根本不使用superior来定义baseds，你可以完全忽略前向声明 - 对于superior的定义你需要 baseds的定义，因为您拥有该类型的成员，因此前向声明是不够的。

Answer 3

对不起堆叠流量的公民，这是一个愚蠢的问题，在睡了一觉之后想出了大部分的错误正确的代码如下：

#include <iostream>
#include <fstream>
#include <boost/archive/text_iarchive.hpp>
#include <boost/archive/text_oarchive.hpp>

class baseds;
class superior;

class baseds {
private:
    friend class boost::serialization::access;
public:
    int a;
    int b;
    int c;
    baseds(){}
    ~baseds(){}
    template <class Archive>
    void serialize(Archive & ar, const unsigned int version)
    {
        ar & a;
        ar & b;
        ar & c;
    }
};

class superior  {
private:
    friend class boost::serialization::access;
    friend class baseds;
public:
    int x;
    int y;
    baseds lag;
    superior(){}
    ~superior(){}
    template <class Archive>
    void serialize(Archive & ar, const unsigned int version)
    {
        ar & x;
        ar & y;
        ar & lag;
    }
};

int main()  {

    superior myData,myData2;
    myData.x=10;
    myData.y=20;
    myData.lag.a=1;
    myData.lag.b=2;
    myData.lag.c=3;

    std::ofstream ofs("steps.txt");
    {
        boost::archive::text_oarchive one(ofs);
        one << myData;
    }

    std::ifstream ifs("steps.txt");
    {
        boost::archive::text_iarchive two(ifs);
        two >> myData2;
    }
    std::cout<<"\n"<<myData2.x;
    std::cout<<"\n"<<myData2.y;
    std::cout<<"\n"<<myData2.lag.a;
    std::cout<<"\n"<<myData2.lag.b;
    std::cout<<"\n"<<myData2.lag.c;

    return 0;

}

当我将一个类声明为其他类的成员时，我收到一个错误。错误：声明朋友时必须使用类键

3 个答案: