CODEWITHSUNDEEP
c++protocol-buffers
Ben
Ben

Reputation: 2937

Google Protocol Buffers in C++: Creating a message from an existing struct

I'm considering Google protocol buffers as a solution to my problem of communication between C++ and C# using named pipes. But I have one concern: all I've been able to find on protobuf is how to create a message from a prototype using protobuf compiler. This is neat, but I would also need to be able to serialize existing structs. I can't seem to find any info (but maybe I'm overlooking it). Do you know if it is possible to serialize a struct in C++ using protobufs, so it can be read in .NET, without modifying said existing struct?

Upvotes: 3

Views: 3496

Answers (1)

Mikael Persson
Mikael Persson

Reputation: 18572

Yes and no.

It's possible. In fact, I have done it. Not the .NET loading part, but the serialization to protobuf and the generation of a prototype from a C++ class. However, doing so requires a number of things and is not that easy.

First of all, protobufs are quite limited in their ability to represent data. They are basically only capable of representing POD-types (in the C++ sense), and very little else. I personally had to add a few basic things to the format to make it into a proper full-featured serialization format. But if you restrict yourself to POD-types, then the plain protobuf format will work fine.

The second thing is that you'll need a serialization library of some kind, and that will require that you add some code for each struct / class to perform the serialization / de-serialization (not necessarily "intrusively", meaning that you might not have to change the classes, just add some code on the side). You can look at Boost.Serialization, that's the basic template for how to create a serialization library in C++. Boost.Serialization is not particularly flexible for this purpose, and so, you might have to change a few things (like I had to do).

The third thing is that you will need quite a bit of wizardry under-the-hood to make this happen. In particular, you are going to need a reliable and feature-rich run-time type identification system (RTTI) in order to able to have useful type names, and you might need to clever meta-programming or some intrusive class hierarchy to be able to detect user-defined types for which you need to generate a prototype.

So, that's why my answer is "yes and no" because it is possible, but not without quite a bit of work and a good framework to rely on.

N.B.: Writing code to encode/decode data into the proto-buf format (with those small-ints, and all that) is really the easy part, proto-buf format is so simple, it's almost laughable. Writing the serialization framework that will allow you to do fancy things like generating prototypes, that's the hard part.

Upvotes: 6

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