C++ 序列化 serialization 如何将类持久化?
C++的類的持久化可以通過下面文章中所使用的方法來實現
其原理是將對象的內容以二進制的形式保存到文件中,
在要讀取的時候再使用相反的過程來加載到對象中.
總結起來就是可以為要進行持久化的對象,比如說配置類,添加如下的兩個方法:
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;
}
參考文章:
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;
?
}
?
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