Find all keys JSON - RapidJSON - c++

Question

I need to find all the keys in the kTypeNames[] with rapidJSON library.
Trying to iterate all the nodes but I'm missing something; here's the code:
#include <iostream>
#include <fstream>
#include <string>
#include <bits/stdc++.h>
#include <unistd.h>
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
using namespace rapidjson;
using namespace std;
const char* kTypeNames[] = { "id", "text", "templ_text", "key" };
int main(int argc, char* argv[]) {
string line;
char json[65000];
std::ifstream file(argv[1]);
unsigned long i = 0;
if (file.is_open()) {
while (!file.eof()) {
file.get(json[i]);
i++;
}
file.close();
} else {
cout << "Unable to open file";
}
Document document;
document.Parse(json);
printf("\n\n\n\n*********Access values in document**********\n");
assert(document.IsObject());
for (auto Typename : kTypeNames) {
if (document.HasMember(Typename)) {
cout << "\n";
cout << Typename << ":" << document[Typename].GetString()<< endl;
cout << "\n";
}
else {
cout << "\n None\n";
}
}
It does not works with a nested JSON.
{
"node": {
"text": "find this",
"templ_text": "don't find",
"ver": "don't find"
},
"ic": "",
"text": "also this",
"templ_text": "don't care",
"par": {
"SET": {
"vis": "<blabla>",
"text": "keyFound",
"templ_text": "don't need this"
}
}
}
This is the output:
None
text:also this
templ_text:don't care
None
I would like to find all the "text" keys
How can I iterate through all the nodes/ json document?

Answer 1

The code you have is just searching for a list of pre-defined keys directly within the document root (document.HasMember is not a recursive search!).
You could just loop through the document nodes recursively. For example for object/map nodes, you loop on the MemberBegin() and MemberEnd() iterators, similar to a std::map or other standard containers.
for (auto i = node.MemberBegin(); i != node.MemberEnd(); ++i)
{
std::cout << "key: " << i->name.GetString() << std::endl;
WalkNodes(i->value);
}
Array uses Begin() and End(). Then, when you encounter a node with a "text" member, you can output the value of that node (i->value).
Alternatively, rather than using a Document DOM object, you can do it with the parser stream. Rapidjson uses a "push" API for this, where it calls methods you define in a class as it encounters each piece of JSON. Specifically, it will call a Key method.
class MyHandler : public BaseReaderHandler<UTF8<>, MyReader> {
bool Key(const char* str, SizeType length, bool copy)
{
std::cout << "Key: " << str << std::endl;
}
...
};
MyHandler handler;
rapidjson::Reader reader;
rapidjson::StringStream ss(json);
reader.Parse(ss, handler);
This gets a bit more complex, you will want to set a flag of some sorts, and then output the next value callback after.
class MyHandler : public BaseReaderHandler<UTF8<>, MyReader> {
bool Key(const char* str, SizeType length, bool copy)
{
isTextKey = strcmp(str, "text") == 0; // Also need to set to false in some other places
return true;
}
bool String(const char* str, SizeType length, bool copy)
{
if (isTextKey) std::cout << "text string " << str << std::endl;
return true;
}
...
bool isTextKey = false;
};
Also remember, that JSON allows a null within a string \0, which is why also have the size parameters and members, as well as Unicode. So to fully support any JSON document that needs accounting for.