C++ 序列化 serialization 如何将类持久化?

C++的类的持久化可以通过下面文章中所使用的方法来实现

其原理是将对象的内容以二进制的形式保存到文件中,

在要读取的时候再使用相反的过程来加载到对象中.

总结起来就是可以为要进行持久化的对象,比如说配置类,添加如下的两个方法:

bool Config::Save()
{
 ofstream ofs("config.bin", ios::binary);
 ofs.write((char *)this, sizeof(*this));
 return true;
}

bool Config::Load()
{
 ifstream ifs("config.bin", ios::binary); 
 ifs.read((char *)this, sizeof(*this));
 return true;
}

参考文章:

Introduction

The C++ language provides a somewhat limited support for file processing. This is probably based on the time it was conceived and put to use. Many languages that were developed after C++, such as (Object) Pascal and Java provide a better support, probably because their libraries were implemented as the demand was made obvious. Based on this, C++ supports saving only values of primitive types such as short, int, char double. This can be done by using either the C FILE structure or C++' own fstream class.

Binary Serialization

Object serialization consists of saving the values that are part of an object, mostly the value gotten from declaring a variable of a class. AT the current standard, C++ doesn't inherently support object serialization. To perform this type of operation, you can use a technique known as binary serialization.

When you decide to save a value to a medium, the fstream class provides the option to save the value in binary format. This consists of saving each byte to the medium by aligning bytes in a contiguous manner, the same way the variables are stored in binary numbers.

To indicate that you want to save a value as binary, when declaring the ofstream variable, specify the ios option as binary. Here is an example:

#include <fstream>

 

#include <iostream>

 

using namespace std;

 

 

 

class Student

 

{

 

public:

 

        char   FullName[40];

 

        char   CompleteAddress[120];

 

        char   Gender;

 

        double Age;

 

        bool   LivesInASingleParentHome;

 

};

 

 

 

int main()

 

{

 

        Student one;

 

 

 

        strcpy(one.FullName, "Ernestine Waller");

 

        strcpy(one.CompleteAddress, "824 Larson Drv, Silver Spring, MD 20910");

 

        one.Gender = 'F';

 

        one.Age = 16.50;

 

        one.LivesInASingleParentHome = true;

 

       

 

        ofstream ofs("fifthgrade.ros", ios::binary);

 

 

 

        return 0;

 

}

Writing to the Stream

The ios::binary option lets the compiler know how the value will be stored. This declaration also initiates the file. To write the values to a stream, you can call the fstream::write()method.

After calling the write() method, you can write the value of the variable to the medium. Here is an example:

#include <fstream>

 

#include <iostream>

 

using namespace std;

 

 

 

class Student

 

{

 

public:

 

        char   FullName[40];

 

        char   CompleteAddress[120];

 

        char   Gender;

 

        double Age;

 

        bool   LivesInASingleParentHome;

 

};

 

 

 

int main()

 

{

 

        Student one;

 

 

 

        strcpy(one.FullName, "Ernestine Waller");

 

        strcpy(one.CompleteAddress, "824 Larson Drv, Silver Spring, MD 20910");

 

        one.Gender = 'F';

 

        one.Age = 16.50;

 

        one.LivesInASingleParentHome = true;

 

       

 

        ofstream ofs("fifthgrade.ros", ios::binary);

 

 

 

        ofs.write((char *)&one, sizeof(one));

 

 

 

        return 0;

 

}

Reading From the Stream

Reading an object saved in binary format is as easy as writing it. To read the value, call the ifstream::read() method. Here is an example:

#include <fstream>

 

#include <iostream>

 

using namespace std;

 

 

 

class Student

 

{

 

public:

 

        char   FullName[40];

 

        char   CompleteAddress[120];

 

        char   Gender;

 

        double Age;

 

        bool   LivesInASingleParentHome;

 

};

 

 

 

int main()

 

{

 

/*      Student one;

 

 

 

        strcpy(one.FullName, "Ernestine Waller");

 

        strcpy(one.CompleteAddress, "824 Larson Drv, Silver Spring, MD 20910");

 

        one.Gender = 'F';

 

        one.Age = 16.50;

 

        one.LivesInASingleParentHome = true;

 

       

 

        ofstream ofs("fifthgrade.ros", ios::binary);

 

 

 

        ofs.write((char *)&one, sizeof(one));

 

*/

 

        Student two;

 

 

 

        ifstream ifs("fifthgrade.ros", ios::binary);

 

        ifs.read((char *)&two, sizeof(two));

 

 

 

        cout << "Student Information/n";

 

        cout << "Student Name: " << two.FullName << endl;

 

        cout << "Address:      " << two.CompleteAddress << endl;

 

        if( two.Gender == 'f' || two.Gender == 'F' )

 

               cout << "Gender:       Female" << endl;

 

        else if( two.Gender == 'm' || two.Gender == 'M' )

 

               cout << "Gender:       Male" << endl;

 

        else

 

               cout << "Gender:       Unknown" << endl;

 

        cout << "Age:          " << two.Age << endl;

 

        if( two.LivesInASingleParentHome == true )

 

               cout << "Lives in a single parent home" << endl;

 

        else

 

               cout << "Doesn't live in a single parent home" << endl;

 

       

 

        cout << "/n";

 

 

 

        return 0;

 

}