How to know count of JSON objects in the file? - c++

Question

I have JSON file
{
"media": [
{
"id": 1234,
"order": 1,
},
{
"id": 1385,
"order": 3,
},
{
"id": 1289,
"order": 2,
}
]
}
with 3 blocks (objects) with the same fileds name ("id", "order"). In the presented example we have 3 blocks. I want to get 3 as answer for my request. How can I do it? If it possible, with the boost library. Next time I'll get another JSON file witch will contains 4 or 5 same blocks
{
"id": 1234,
"order": 1,
},
and I want to know count of those blocks in the JSON file

Answer 1

Simplest: Live On Compiler Explorer
#include <boost/json/src.hpp>
static auto sample = R"({
"media": [{
"id": 1234,
"order": 1,
},
{
"id": 1385,
"order": 3,
},
{
"id": 1289,
"order": 2,
}]
})";
int main() {
auto v = boost::json::parse(sample, {}, {.allow_trailing_commas=true});
return v.at("media").as_array().size();
}
Returns 3
Note that there are much more efficient ways to do it using e.g. https://www.boost.org/doc/libs/1_79_0/libs/json/doc/html/json/ref/boost__json__stream_parser.html or even just https://www.boost.org/doc/libs/1_79_0/libs/json/doc/html/json/ref/boost__json__basic_parser.html