How to Skip Parsing of Token in Rapidjson - c++

Question

I have to Parse only certain Tokens in Data Structure using RapidJson.And skip other tokens to save time.
For eg. How to parse only "t" token without parsing other tokens
{
"hello": "world",
"t": true ,
"f": false,
"n": null,
}
I am using Iterative Parsing ,How do I parse only a certain token 'Key' .I have tried checking the 'Key' value to my required token and then retuening from code but program stopped executing.
struct MyHandler : public BaseReaderHandler<UTF8<>, MyHandler> {
bool Null() { cout << "Null()" << endl; return true; }
bool Bool(bool b) { cout << "Bool(" << boolalpha << b << ")" << endl; return true; }
bool Int(int i) { cout << "Int(" << i << ")" << endl; return true; }
bool Uint(unsigned u) { cout << "Uint(" << u << ")" << endl; return true; }
bool Int64(int64_t i) { cout << "Int64(" << i << ")" << endl; return true; }
bool Uint64(uint64_t u) { cout << "Uint64(" << u << ")" << endl; return true; }
bool Double(double d) { cout << "Double(" << d << ")" << endl; return true; }
bool String(const char* str, SizeType length, bool copy) {
cout << "String(" << str << ", " << length << ", " << boolalpha << copy << ")" << endl;
return true;
}
bool StartObject() { cout << "StartObject()" << endl; return true; }
bool Key(const char* str, SizeType length, bool copy) {
cout << "Key(" << str << ", " << length << ", " << boolalpha << copy << ")" << endl;
return true;
}
bool EndObject(SizeType memberCount) { cout << "EndObject(" << memberCount << ")" << endl;
return true; }
bool StartArray() { cout << "StartArray()" << endl; return true; }
bool EndArray(SizeType elementCount) { cout << "EndArray(" << elementCount << ")" << endl;
return true; }
};
//char* readBuffer is my json data in char array
MyHandler handler;
Reader reader;
StringStream ss(readBuffer);
reader.IterativeParseInit();
while (!reader.IterativeParseComplete()) {
reader.IterativeParseNext<kParseDefaultFlags>(ss, handler);
}
Thank You

Answer 1

You must maintain a state in your Handler set / unset depending if you have encountered the key you want to pass.
It is not straightforward because you must take into account that you can encounter the same key at various (nested) level.
If really you want to continue in this direction you can have a look in rapidjson example here https://github.com/Tencent/rapidjson/tree/master/example/filterkey
This make the opposite of your need, parsing everything except the given key. That should give you a good starting point.
Another solution is to use DOM parsing and "clean" after parsing the unwanted keys, which is much more easier. Off course it will not have the same performance but at least you will free memory associated with token you do not need.
auto itr = myDoc.MemberBegin();
while (itr != myDoc.MemberEnd())
{
if (itr->name == "keyIWantToKeep")
itr++;
else
itr = myDoc.EraseMember(itr);
}