Access fields of a JSON array using RapidJSON in C++ - c++

Question

I am new using the RapidJSON library and I want to know how I can access specific elements within an array in JSON format, this is the JSON:
{
"products": [
{
"id_product": 1,
"product_name": "Beer",
"product_price": 120.00
},
{
"id_product": 2,
"product_name": "Pizza",
"product_price": 20.00
}
]
}
I have this part of the code to make:
Document json_value;
json_value.Parse(json_message); //Above Json
if(!json_value.IsObject())
{
//ERROR
}
if(json_value.HasMember("products"))
{
const Value& a = json_value["products"];
if(a.IsArray())
{
for (SizeType i = 0; i < a.Size(); i++)
{
//Here i dont know how to access the elements of the array elements, but i need something like this:
int element_id = 1; //id_product = 1
string element_name = "Beer"; // product_name = "Beer"
float element_price = 120.00; //prodcut_price = 120.00
}
}
}

Answer 1

You can access the elements of the object using operator[]().
for (SizeType i = 0; i < a.Size(); i++)
{
if (a[i].IsObject()) {
int element_id = a[i]["id_product"].GetInt();
string element_name = a[i]["product_name"].GetString();
double element_price = a[i]["product_price"].GetDouble();
}
}
Please note that you might want to add checks for the type and existence of the member if your JSON is not always consistent.

Answer 2

Since for each "product" in products is an object, you can also iterate each key,value pair like this:
const Value& products = json_value["products"];
for (auto& product: products) { // products is type Array
for (auto& prod : product.GetObject()) {
std::cout << prod.name // similar to map->first
// i.e "id_product", "product_name"
<< prod.value // similar to map->second
// i.e 2, "Pizza"
<< std::endl;
}
}

Answer 3

I believe you can just call operator[]() with an unsigned int, if the value is an array. The tutorial appears to confirm this:
const Value& a = document["a"];
assert(a.IsArray());
for (SizeType i = 0; i < a.Size(); i++) // Uses SizeType instead of size_t
printf("a[%d] = %d\n", i, a[i].GetInt());
You can also get iterators using MemberBegin() and MemberEnd().