Iterate over an array of JSON objects with jsoncpp

Question

I have an array of JSON objects, jsonArr say, of the following kind:

[
  { "attr1" : "somevalue",
    "attr2" : "someothervalue"
  },
  { "attr1" : "yetanothervalue",
    "attr2" : "andsoon"
  },
  ...
]

Using jsoncpp, I'm trying to iterate through the array and check whether each object has a member "attr1", in which case I would like to store the corresponding value in the vector values.

I have tried things like

Json::Value root;
Json::Reader reader;
Json::FastWriter fastWriter;
reader.parse(jsonArr, root);

std::vector<std::string> values;

for (Json::Value::iterator it=root.begin(); it!=root.end(); ++it) {
  if (it->isMember(std::string("attr1"))) {
    values.push_back(fastWriter.write((*it)["uuid"]));
  }
}

but keep getting an error message

libc++abi.dylib: terminating with uncaught exception of type Json::LogicError: in Json::Value::find(key, end, found): requires objectValue or nullValue

Sga · Accepted Answer · 2017-07-11 14:29:56Z

18

Pretty self explanatory:

for (Json::Value::ArrayIndex i = 0; i != root.size(); i++)
    if (root[i].isMember("attr1"))
        values.push_back(root[i]["attr1"].asString());

answered Jul 11, 2017 at 14:29

Sga

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Comments

rbaleksandar · Accepted Answer · 2023-03-22 12:56:04Z

2

Alternatively to what @Sga suggested I would recommend using a ranged for loop:

for (auto el : root)
{
  if (el.isMember("attr1"))
    values.push_back(el["attr1"].asString());
}

I find this to be more readable plus it saves the extra call on size() as well as the index-wise retrieval.

answered Mar 22, 2023 at 12:56

rbaleksandar

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