Question

Firstly, I know that writing a class to disk is bad, but you should see some of our other code. D:

My question is: can I write a polymorphic class to disk and then read it in later and not get undefined behaviour? I am going to guess not because of vtables (I think these are generated at runtime and unique to the object?)

I.e.

class A {
    virtual ~A() {}
    virtual void foo() = 0;
};

class B : public A {
    virtual ~B() {}
    virtual void foo() {}
};

A * a = new B;

fwrite( a, 1, sizeof( B ), fp );

delete a;

a = new B;

fread( a, 1, sizeof( B ), fp );

a->foo();

delete a;

Thank-you!

Answer 1

I’ll suggest you to take a look at Boost Serialization.

we use the term “serialization” to mean the reversible deconstruction of an arbitrary set of C++ data structures to a sequence of bytes. Such a system can be used to reconstitute an equivalent structure in another program context. Depending on the context, this might used implement object persistence, remote parameter passing or other facility.