C++ JSON Serialization

For that you need reflection in C/C++, which doesn’t exist. You need to have some meta data describing the structure of your classes (members, inherited base classes). For the moment C/C++ compilers don’t automatically provide that information in built binaries.

I had the same idea in mind, and I used GCC XML project to get this information. It outputs XML data describing class structures. I have built a project and I’m explaining some key points in this page :

Serialization is easy, but we have to deal with complex data structure implementations (std::string, std::map for example) that play with allocated buffers. Deserialization is more complex and you need to rebuild your object with all its members, plus references to vtables … a painful implementation.

For example you can serialize like this:

    // Random class initialization
    com::class1* aObject = new com::class1();

    for (int i=0; i<10; i++){
            aObject->setData(i,i);
    }      

    aObject->pdata = new char[7];
    for (int i=0; i<7; i++){
            aObject->pdata[i] = 7-i;
    }
    // dictionary initialization
    cjson::dictionary aDict("./data/dictionary.xml");

    // json transformation
    std::string aJson = aDict.toJson<com::class1>(aObject);

    // print encoded class
    cout << aJson << std::endl ;

To deserialize data it works like this:

    // decode the object
    com::class1* aDecodedObject = aDict.fromJson<com::class1>(aJson);

    // modify data
    aDecodedObject->setData(4,22);

    // json transformation
    aJson = aDict.toJson<com::class1>(aDecodedObject);
   
    // print encoded class
    cout << aJson << std::endl ;

Ouptuts:

>:~/cjson$ ./main
{"_index":54,"_inner":  {"_ident":"test","pi":3.141593},"_name":"first","com::class0::_type":"type","com::class0::data":[0,1,2,3,4,5,6,7,8,9],"com::classb::_ref":"ref","com::classm1::_type":"typem1","com::classm1::pdata":[7,6,5,4,3,2,1]}
{"_index":54,"_inner":{"_ident":"test","pi":3.141593},"_name":"first","com::class0::_type":"type","com::class0::data":[0,1,2,3,22,5,6,7,8,9],"com::classb::_ref":"ref","com::classm1::_type":"typem1","com::classm1::pdata":[7,6,5,4,3,2,1]}
>:~/cjson$

Usually these implementations are compiler dependent (ABI Specification for example), and require external descriptions to work (GCCXML output), thus are not really easy to integrate to projects.

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