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# C++ XML Serialization

## 5 posts in this topic

As a learning exercise to get more familiar with C++, I'm trying to Serialize a class to xml but finding its quite intimidating than what i'm used to with c#..

class Level : public DrawableObject {
public:
std::vector<Sprite> spritelist;
int sizeX;
int sizeY;
int tileSize;
Level();
};


What would be ideal is to have a library come in and have a look at the class and convert each field it to xml. (which apparently would be to much to hope for lol).

My major concern with trying to manually specify what to serialize is when it comes to the spritelist vector that it wont serialize the Sprite Classes.

Does anyone have any suggestions to frameworks and implementations?.

Edited by Mellkor
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You could include the serialization logic inside the Sprite class itself, and then go through your vector asking them to serialize themselves passing a XML reference for it to use...

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Maybe you can give cereal a try. It should be pretty easy to save it as a XML file.
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What would be ideal is to have a library come in and have a look at the class and convert each field it to xml. (which apparently would be to much to hope for lol).

This is not possible in C++ today, though some proposals for the next upcoming version (C++17) may change this. For now, you need to explicitly tell external libraries about each field or write a custom serialization function that serializes the fields. A common idiom is something like:

void Serialize(Level& level, Serializer& serial) {
serial.Serialize("spriteList", level.spriteList);
serial.Serialize("sizeX", level.sizeX);
serial.Serialize("sizeY", level.sizeY);
serial.Serialize("tileSize", level.tileSize);
}
class Serializer {
public:
virtual void Serialize(const char* name, int& value) = 0;
virtual void Serialize(const char* name, float& value) = 0;
... other serializable type overloads ...
};

class XmlSerializeWriter final : public Serializer {
public:
void Serialize(const char* name, int& value) override { write_int_element(name, value); }
... etc ...
};

class SerializeReader final : public Serializer {
void Serialize(const char* name, int& value) override { value = read_int_element(name); }
... etc ...
};
XmlSerializeWriter writer{... initialize params, path, etc. ...};
Serialize(level, writer); // writes out an existing level
XmlSerializeReader reader{... initialize params, path, etc. ...};
Level level;
Serialize(level, reader); // reads in a level
With some work, you can handle containers (vector, deque, unordered_map, etc.), custom types, etc. Games typically work with a fairly restricted vocabulary of serializable types so it's not too bad.
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The best methods I could come up with in terms of "minimal extra work" either involve defining the class wrapped in ugly macros like

SER_CLASS(Classname)

{

SER_MEMBER(int, a)

SER_MEMBER(std::string, b)

}

or would involve some arcane meta-programming based on boost fusion and still requires to "tell" what the class looks like. So either you'll end up defining all members twice (for the actual class and the adapted struct) or again using macros to automatically creating both at the same time.

Chances are that creating that kind of framework will take a lot of time and then be inflexible enough to cause more problems than it solves.

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I developed a solution a while back that works relatively well in practice, and I've been using it at work for some time now. It's targeted towards JSON via JsonCpp, but the basic ideas should be adaptable. It is not simple, leaning on some fairly arcane C++/template stuff.

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