Reading/writing files to/from a struct/class

Question

I\'d like to read a file into a struct or class, but after some reading i\'ve gathered that its not a good idea to do something like:

int MyClass::loadFile(          


        

Answer 1

The preferred general technique is called serialization.

It is less brittle than a binary representation. But it has the overhead of needing to be interpreted. The standard types work well with serialization and you are encouraged to make your class serialize so that a class containing your class can easily be serialized.

class MyClass {
     int x;
     float y;
     double z;
     friend std::ostream& operator<<(std::ostream& s, MyClass const& data);
     friend std::istream& operator>>(std::istream& s, MyClass& data);
};

std::ostream& operator<<(std::ostream& s, MyClass const& data)
{
    // Something like this
    // Be careful with strings (the input>> and output << are not symmetric unlike other types)
    return str << data.x << " " << data.y << " " << data.z << " ";
}

// The read should be able to read the version printed using <<
std::istream& operator>>(std::istream& s, MyClass& data)
{
    // Something like this
    // Be careful with strings.
    return str >> data.x >> data.y >> data.z;
}

Usage:

int main()
{
    MyClass   plop;
    std::cout << plop;  // write to a file
    std::cin  >> plop;  // read from a file.


    std::vector  data;

    // Read a file with multiple objects into a vector.
    std::ifstream  loadFrom("plop");
    std::copy(std::istream_iterator(loadFrom), std::istream_iterator(),
              std::back_inserter(data)
             );


    // Write a vector of objects to a file.
    std::ofstream   saveTo("Plip");
    std::copy(data.begin(), data.end(), std::ostream_iterator(saveTo));

    // Note: The stream iterators (std::istream_iterator) and (std::ostream_iterator)
    //       are templatized on your type. They use the stream operators (operator>>)
    //       and (operator<<) to read from the stream.
}