How to distinguish Object from Array in Poco C++ without exception catch

Question

As we have already know, we use following code for parsing json data

std::string jsonString = "{\"aa\":\"bb\"}";
Poco::JSON::Parser parser;
Poco::Dynamic::Var result;
result = parser.parse(jsonString);
Poco::JSON::Object::Ptr pObj = result.extract<Poco::JSON::Object::Ptr>();
... // goes with pObj

We know "{\"aa\":\"bb\"}" is json object, so we use result.extract

and following code for parsing json array data

std::string jsonString = "[{\"aa\":\"bb\"}, {\"cc\":\"dd\"}]";
Poco::JSON::Parser parser;
Poco::Dynamic::Var result;
result = parser.parse(jsonString);
Poco::JSON::Array::Ptr pArr = result.extract<Poco::JSON::Array::Ptr>();
... // goes with pArr

we know "[{\"aa\":\"bb\"}, {\"cc\":\"dd\"}]", so we use result.extract

So, my first thought is:

... 
try {
    Poco::JSON::Object::Ptr pObj = result.extract<Poco::JSON::Object::Ptr>(); // this does be a json object
} catch (...) {}

try {
    Poco::JSON::Array::Ptr pArr = result.extract<Poco::JSON::Array::Ptr>(); // this does be a json array
} catch (...) {}
...

Then, Using code above with exception catch, I can distinguish Object from Array.

So, is there any way that solving this kind question without exception catch?

Answer 1

Use C++'s type info to solve this problem

std::string jsonString = "[{\"aa\":\"bb\"}, {\"cc\":\"dd\"}]";
// or std::string jsonString = "{{\"aa\":\"bb\"}, {\"cc\":\"dd\"}}";

try {
    result = parser.parse(jsonString);
} catch (Poco::SyntaxException & e) {
    std::cout << "This is not a valid json data" << std::endl;
    return;
}

Poco::JSON::Array::Ptr p;

if (typeid(p) == result.type()) {
    std::cout << "This is a arry"  << std::endl;
} else {
    std::cout << "This is a object"  << std::endl;
}