serializeJson() only prints the first characters of strings on Arduino Due

[sezaicelikdogan]

Starting from version 7.2.1 and above serializeJson(doc, Serial) do not create pair names correctly. Only the first letters of the value pairs are stored.

For example:
doc["cat"] = "sensor";
doc["type"] = "rpm";

is serialized as {"c":"s","t":"r"}

below 7.2.1 this problem not occurs

[bblanchon]

It works fine here: https://wandbox.org/permlink/fv1IVJA0QIB6bdN6
Please provide an MCVE.

[sezaicelikdogan]

Platform : Arduino ide 2.3.6
OS : windows 11
ArduinoJson Lib : 7.4.1

Code :
#include <ArduinoJson.h>

void setup() {
Serial.begin(115200);
while (!Serial)
continue;
}

void loop() {
JsonDocument doc;
doc["sensor"] = "gps";
doc["type"] = "rpm";
serializeJson(doc, Serial);
delay(1000);
}

Serial monitor output :
{"s":"g","t":"r"}{"s":"g","t":"r"}...

[atwalsh]

I had the same issue on the Particle platform. Got around it by following this thread on the Particle forums.

Try changing doc["cat"] to doc[String("cat")].

Note, I am also setting ARDUINOJSON_ENABLE_ARDUINO_STRING to 1.

[bblanchon]

I successfully tested the program above with the following boards:

1. Arduino Leonardo
2. Arduino UNO R4 WiFi
3. Adafruit ESP8266 Feather Huzzah
4. A generic ESP32

My setup:

• ArduinoJson 7.4.1
• Arduino IDE 2.3.6
• Windows 11
• All cores updated to the latest version

@sezaicelikdogan, @atwalsh, please provide more information about your setup.
Also, please try to uninstall and reinstall the library.

[sezaicelikdogan]

Sorry I forgot to write :
Board : Arduino Due (original)

I uninstall and reinstall the lib but still give the same error.

[sezaicelikdogan]

I had the same issue on the Particle platform. Got around it by following this thread on the Particle forums.

Try changing doc["cat"] to doc[String("cat")].

Note, I am also setting ARDUINOJSON_ENABLE_ARDUINO_STRING to 1.

This solved the problem.

and also I wrote the same for the valu 👍

doc[String("cat")] = String("sensor")

[bblanchon]

@atwalsh, using String is slower than using string literal, produces larger code, and increases heap fragmentation, so you should only use this as a temporary fix until we fully understand what's happening.

@sezaicelikdogan, I don't own an Arduino Due, and unfortunately, the Due has a dedicated core that isn't shared with any other board.
Could you try on a different board?

[bblanchon]

I also successfully tested on:

5. Arduino MKR1000 WiFi
6. Adafruit ItsyBitsy M4
7. Teensy 3.1
8. Nucleo-32
9. Teensy 4.1
10. Arduino Nano Every

[sezaicelikdogan]

@atwalsh, using String is slower than using string literal, produces larger code, and increases heap fragmentation, so you should only use this as a temporary fix until we fully understand what's happening.

@sezaicelikdogan, I don't own an Arduino Due, and unfortunately, the Due has a dedicated core that isn't shared with any other board. Could you try on a different board?

Thanks for your kind info. I can try with other boards of course and I will soon inform the result, but unfortunately this project has to be done with Arduino Due and if problem can not be corrected than I have to continue with creating the json string manually. But thanks for your efforts.