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;
}