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saving objects

Hi,

I wish to save some objects in a data file to make the state of an application persistent. Is this possible in c++? As things stand I have one main object with member variables of different classes built into it. For example, class main has a vector<Person> people; in it. I simply wish to store main transparently in a file and recreate it with the exact state of the object and all its sub objects intact. Am I allowed or is there some more low level facility? I have used Java in the past and ObjectStreams, or something similar, so would like a c++ equivalent.

Thanks for any help.

Axter

>>Is this possible in c++?
Yes

>>Am I allowed or is there some more low level facility?

You can do this by creating and operator>>() and an operator<<() function for your class.

These functions would then read and write data for your class.

Axter

If you're using MFC, you can use CObject with Serialize member function.

What type of application do you have, and what compiler are you using?

Axter

Here's some example code for using operator>>() and operator<<()

class person
{
public:
      person(const std::string& Name, int Age)
            :m_Name(Name), m_Age(Age)
      {
      }
      person()
            :m_Age(0)
      {
      }
      friend ostream& operator<<(ostream& s, const person & src)
      {
            s << src.m_Name << "\t" << src.m_Age << "\t";
            return s;
      }
      friend istream& operator>>(istream& s, person & src)
      {
            std::getline(s, src.m_Name, '\t');
            std::string Age;
            std::getline(s, Age, '\t');
            src.m_Age = atoi(Age.c_str());
            return s;
      }
private:
      std::string m_Name;
      int m_Age;
};

int main(int argc, char* argv[])
{
      person MyPerson1("David Axter", 43);
      person MyPerson2("Bush Stinks", 23);
      person MyPerson3("(ABB) anything but bush", 11);
      cout << MyPerson1 << endl;
      cout << MyPerson2 << endl;
      cout << MyPerson3 << endl;

      fstream file;
      file.open("c:\\testx.txt", ios_base::out);
      file << MyPerson1;
      file << MyPerson2;
      file << MyPerson3;
      file.close();

      cout << endl << endl << endl;
      file.open("c:\\testx.txt", ios_base::in);
      person MyPerson_Copy[3];
      for (int i = 0;i < 3;++i)
      {
            file >> MyPerson_Copy[i];
            cout << MyPerson_Copy[i] << endl;
      }

      system("pause");
      return 0;
}

jasoncpp

ASKER

Didn't realise I would have to overload the << and >> operators, least I know now, thanks. The main object isnt an mfc one, I am using mfc. Could the mfc serialize make my task easier for non-mfc objects or must I serialize every class as explained?

I'm using VC++ 6.

Secondly, can you give me a quick code example of Person having another custom class as its attribute, for example, Car or anythign else please? I just want to clarify how compound objects get saved using << >>.

Cheers.

bkfirebird

like Axter said, you can derive any class from CObject and make it serializable

ASKER CERTIFIED SOLUTION

Axter

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Axter

When using stream to save and retrieve objects, a key thing to keep in my is that you need to use a character that will seprate the objects.
What ever character you use for object seperation, can not be a character that could possibly be part of the object.
Example, you can't use a space for the object sperator, because Name object would have a space in it for First and Last name.

Also, you usually want each complex object resposible for it's own read/write stream operations.

As you can see with the example code, the nice thing about this method, is that it lets you use the code for sending the data to a file, and for sending it to the screen.

jasoncpp

ASKER

Great stuff and amusing too! You have been very helpful. Thanks :)