How do I save and load a std::string with object serialization in C++?

Question

I had something simple like this POD structure...

struct Actor
{
    string name; 
    int hp;
};

Later on, for simplicity sake here, I saved the structure to file using...

 ofstream_obj.write((char *)&PC, sizeof(Actor));

Then, I tried reading the file back. It loaded in the data, but upon exit it gave an ugly exception, pointing at xutility at the line of: *_Pnext != 0

inline void _Container_base12::_Orphan_all()
    {   // orphan all iterators
 #if _ITERATOR_DEBUG_LEVEL == 2
    if (_Myproxy != 0)
        {   // proxy allocated, drain it
        _Lockit _Lock(_LOCK_DEBUG);

        for (_Iterator_base12 **_Pnext = &_Myproxy->_Myfirstiter;
            *_Pnext != 0; *_Pnext = (*_Pnext)->_Mynextiter)
            (*_Pnext)->_Myproxy = 0;
        _Myproxy->_Myfirstiter = 0;
        }
 #endif /* _ITERATOR_DEBUG_LEVEL == 2 */
    }

After giving up, I changed the std::string to char name[20], tried the whole thing again, and it worked fine. Is there something different about loading back std::string? Is it not calling std::string's copy constructor?

ratchet freak · Accepted Answer · 2014-04-19 00:27:48Z

3

std::string holds a pointer internally to the actual string data which is malloced on the heap.

write(char*, size_t) doesn't consider internal types (and associated copy constructors) AT ALL. This means that you were writing a pointer to a file, which never works.

to fix it properly you would need actual serialization that writes the string out properly (like write length and then the data)

answered Apr 19, 2014 at 0:27

ratchet freak

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