Cant modify existing numbers inside a json object

[AMScaglione]

Say for example I have something like

json j;
j["num"] = 0;

I can not do something like

j["num"] += 1;

as it gives me this error on runtime:

terminate called after throwing an instance of 'std::domain_error'
  what():  cannot use push_back() with number

I tried simplifying it to

j["num"] = j["num"] + 1;

but that gives me this error at compile time:
error: no match for 'operator+' (operand types are 'nlohmann::basic_json<>::value_type {aka nlohmann::basic_json<>}' and 'int')|

[gregmarr]

j["num"] is a json object, not an int. You need to get() the int out of it before you can add 1 to it and assign it back again.

[nlohmann]

In addition to @gregmarr s remarks: += is an overload for json::push_back and can only be called on a JSON array. And indeed the + operator has no overload for json and int.

To increment j["num"], you need to call

j["num"] = j["num"].get<int>() + 1;

or

j["num"] = int(j["num"]) + 1;

[nlohmann]

@AMScaglione Does this work for you?

[AMScaglione]

Yeah! Sorry, it does

…

On Sat, Apr 22, 2017 at 3:57 AM, Niels Lohmann ***@***.***> wrote: @AMScaglione <https://github.com/AMScaglione> Does this work for you? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#557 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AVcekUst_5M6J6jbdQ9tFlOYcsaSz2kyks5rybL2gaJpZM4M-vei> .

[nlohmann]

No problem.