ESP32

There is currently a bug in the Arduino Core for ESP32 causing the following error:

error: redefinition of 'struct ArduinoJson::Internals::StringFuncs<const char*>'

The solution is to disable PROGMEM support in ArduinoJson. To do that, just add the following line at the top of your program:

#define ARDUINOJSON_ENABLE_PROGMEM 0

Then, you may have the following linker error undefined reference to __cxa_guard_acquire and __cxa_guard_release