Serialise and deserialise vector in binary

Question

I am having problems trying to serialise a vector (std::vector) into a binary format and then correctly deserialise it and be able to read the data. This is my first time us

Answer 1

You can't unserialise a non-POD class by overwriting an existing instance as you seem to be trying to do - you need to give the class a constructor that reads the data from the stream and constructs a new instance of the class with it.

In outline, given something like this:

class A {
    A();   
    A( istream & is );    
    void serialise( ostream & os );
    vector  v;
};

then serialise() would write the length of the vector followed by the vector contents. The constructor would read the vector length, resize the vector using the length, then read the vector contents:

void A :: serialise( ostream & os ) {
    size_t vsize = v.size();    
    os.write((char*)&vsize, sizeof(vsize));
    os.write((char*)&v[0], vsize * sizeof(int) );
}

A :: A( istream & is ) {
    size_t vsize;
    is.read((char*)&vsize, sizeof(vsize));
    v.resize( vsize );
    is.read((char*)&v[0], vsize * sizeof(int));
}