How to serialize Objects in C++ via copying memory?

Question

Is it possible in C++ to serialize an object by taking a pointer of the first address of the object and increment this pointer till the end of the object is reached?

If it's possible, how can I find the first memory adress of the object and in which data type should I store the values? And how could I build the object on the other side?

why do you want to serialize. is it to send the object to another process or computer, or so you can write it to a file? — Scott Langham, Nov 30 '11 at 17:11
Here are some things you'll need to consider: (1) how to deal with classes that have non-trivial constructors; (2) how to deal with pointers/references contained within the object; (3) how to deal with virtual base classes. — NPE, Nov 30 '11 at 17:12

score 3 · Accepted Answer · edited May 23 '17 at 11:55

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This is relatively easy to do in some very restrictive circumstances (POD with no pointers/references; same OS, CPU architecture and the C++ compiler on both ends of the serialization pipe).

There is a number of issues that complicate matters in the more general case:

dealing with classes that have non-trivial constructors/destructors;
dealing with pointers/references contained within the object;
cycles in the pointer/reference graph;
polymorphism;
dealing with virtual base classes;
endianness;
field alignment, padding etc;
the width of primitive types (int on one platform isn't necessarily the same size as int on another);
versioning so that new fields can be added without breaking stuff.

edited May 23 '17 at 11:55

Community

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answered Nov 30 '11 at 17:14

NPE

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Even in a POD containing no pointers or references it can fail due to padding between fields. – Jerry Coffin Nov 30 '11 at 17:21
@Jerry: depends what aix means by, "same OS, CPU architecture and the C++ compiler". If the two implementations share a C ABI, then they'll necessarily have the same layout for POD structs. But compiler options can affect that. – Steve Jessop Nov 30 '11 at 17:38
@SteveJessop: it's pretty common to use things like `#pragma pack` to force a specific alignment for structs used in the ABI, but still have variation in other structs, so sharing an ABI doesn't necessarily mean much. – Jerry Coffin Nov 30 '11 at 18:00

score 2 · Answer 2 · answered Nov 30 '11 at 17:11

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The procedure you describe would create a flat copy of the object. If that object contained pointers or references itself, this scheme would break.

If you want to serialize objects, use a library like Boost.Serialization.

answered Nov 30 '11 at 17:11

Björn Pollex

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And even if it doesn't it's completely non-portable as it exposes implementation details like alignment, padding, endian and the sizes of types. – Laurence Gonsalves Nov 30 '11 at 17:14

score 0 · Answer 3 · answered Nov 30 '11 at 17:11

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There are several serialization formats (XDR, ASN1, JSON, YAML), techniques, and libraries (like s11n for C++)

answered Nov 30 '11 at 17:11

Basile Starynkevitch

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How to serialize Objects in C++ via copying memory?

3 Answers3