Appending an array to a Json Value in C++

Question

I know that if I have some integer 'a' and 'b' that I can append them to a Value in Json:

Value root;
Value v = root["int"];
int a = 1;
int b = 2;
v.append(a);
v.append(b);

Resulting Json file:

"int": 
  [
    1,
    2
  ]

But is there also a way to append entire arrays? Perhaps something like this:

Value root;
Value v = root["arrays"];
int a[3] = {1,2,3};
int b[3] = {4,5,6};
v.append(a);
v.append(b);

I'm trying to have my resulting Json file look like:

"arrays": 
  [
    [1, 2, 3],
    [4, 5, 6]
  ]

But instead, Json only appends the pointer address value, which reads as "true":

"arrays": 
  [
    true,
    true
  ]

Yeah, an extend() is exactly what I'm looking for, but I can't find one within jsoncpp (https://github.com/open-source-parsers/jsoncpp). I don't think copy() helps, because I still can't get that array data into the Json file properly. — Otherness, May 01 '20 at 18:25
hyde: range-for is close, but it just dumps in all the values of the two arrays without structure, like this: "arrays": [ 1, 2, 3, 4, 5, 6 ] — Otherness, May 01 '20 at 18:31

hyde · Accepted Answer · 2020-05-01T18:59:10.787

1

The explicit way is to use range-for with a temp Value.

Value root;
Value v = root["arrays"];
int a[3] = {1,2,3};
int b[3] = {4,5,6};

Value tmp;
for(auto i : a) { tmp.append(i); }
v.append(tmp);

tmp = Value{}; // reset
for(auto i : b) { tmp.append(i); }
v.append(tmp)

A possible helper template function to wrap it nicely:

template<typename RANGE>
Value rangeToValue(RANGE src) {
    Value result;
    for (const auto &value : src) {
        result.append(value);
    }
    return result;
}

Then this should work:

v.append(rangeToValue(a)); v.append(rangeToValue(b));

edited May 01 '20 at 18:59

answered May 01 '20 at 18:24

hyde

60,639
21
115
176

Heck yes! You're my favourite person of the day, hyde. Thanks! – Otherness May 01 '20 at 18:47

Appending an array to a Json Value in C++

1 Answers1