How to properly read a Json string that may be null in some cases?

[TyloowNv]

Hello,

I have some json format texts received as server response and would like to use this tool to parse them. The issue is if the value in a string field is optional and not provided from the server side, client side will receive a null rathe than an empty string. This currently throws exceptions while parsing.

For example this is the code where we read the title of a layer.

bh.layers[j].name = js.at(i)["th_layers"].at(j)["layer_title"].get<string>().c_str();

However, in the json format, sometime the server response could be this. And this can be parsed without any issue.
"layer_title": "Fill Material",
But sometimes it becomes this and throws an exception.
"layer_title": null,

Is there a better way of parsing this null and give a default value(like "" for string and 0 for int) rather than using try and catch?

Thanks a lot!

[gregmarr]

js.at(i)["th_layers"].at(j)["layer_title"]

This is what creates the null "layer_title". You need to check if it exists before you try to get its value.

If js is not const then accessing a non-existent object value creates it, while if it is const it's undefined behavior and asserts.

https://json.nlohmann.me/features/element_access/default_value/