Arduinojson: Converting json response to char[]

[dimityrivanov]

After updating the library this line started to fail

strcpy(customVar.name, mLastRedJsonObject["key"]);

where customVar is a struct where name field is

const char name[20];

Any idea why that is happening when reaching that line the esp8266 is resseting itself

[bblanchon]

Hi @mitko9000,

mLastRedJsonObject["key"] is probably null.
I bet that the DynamicJsonDocument is too small.
Unlike DynamicJsonBuffer, DynamicJsonDocument doesn't grow automatically; you need to pass the right capacity to the constructor.

BTW, your code would be much safer with:

strlcpy(customVar.name, mLastRedJsonObject["key"] | "", sizeof(customVar.name));

Best Regards,
Benoit

[dimityrivanov]

How can I calculate the size of the StaticJsonDocument<100> bytes I need for staticJsonDocument @bblanchon

[bblanchon]

To calculate the capacity of the JsonDocument, use the ArduinoJson Assitant.
@mitko9000, this is written virtually everywhere on the site, how did you miss it?

[dimityrivanov]

@bblanchon thanks for the feedback well my problem is resolved I had to move the StatisJsonDocument to public scope due to the fact I am reusing it, so this can be closed.

Maybe I missed it because I started using the library and reading the migration script but never actually visited the home page, never hurt to ask :D

[bblanchon]

Cool. Thanks for the update.