arduino-libraries
Getting wrong values on double or long parsing and stringify
I'm using the "JSONObject" example with Arduino Nano.
I have changed the following line:
https://github.com/arduino-libraries/Arduino_JSON/blob/ea843a9a0b56e3baaa1d26795072f81b9b8787ca/examples/JSONObject/JSONObject.ino#L13
to:
const char input[] = "{\"result\":true,\"count\":551489800,\"foo\":\"bar\"}";
(changed the value of count from 42 to 551489800)
The value returned is 551489792 on parsing and on stringify.
Using different values, I realize that it seems that the 4th byte of the long or double is not added properly. (OK up to FFFFFF, 3 bytes.) But added investigation shows that the problem occurs on last byte when 4th byte is present.
If I try different "count" values, I get :
| Value | Correctly handled? | Notes |
|---|---|---|
| 20DF1108 | No | Converted to 20DF1100 |
| 20DF1118 | No | Converted to 20DF1100 |
| 20DF10FF | No | Converted to 20DF1100 |
| DF10EF | Yes | |
| FFFFFF | Yes | |
| 1DF13DF | No | Converted to 1DF13E0 |
| 1000000 | Yes | |
| 7000000 | Yes | |
| 7DF10EF | No | converted to 7DF10F0 |
| F000000 | Yes | |
| FDF10EF | No | Converted to FDF10F0 |
| 10000000 | Yes | |
| 100D0000 | Yes | |
| 100D0100 | Yes | |
| 100F10EF | No | converted to 100F10E0 |
I include the modified JSONObject.ino JSONObject.zip
Answering myself. This seems to be the same problem as in https://forum.arduino.cc/index.php?topic=546985.0 It seems the internals of the library does not convert properly as in the previous example. For a quick solution, I use strings (number surrounded by double quotes) instead of a number (without double quotes) to transfer the data and I convert with atol (which does not implement the error) instead of string.toDouble() - which implements the error. (Maybe that's the problem ?) I include a small TestDouble.ino file.
It looks like I'm having the same problem in reverse:
float a1 = 982.661255f;
double b1 = 0.001 * (int)(1000 * a1); // clip some decimals
JSONVar a2 = a1;
JSONVar b2 = b1;
Serial.printf("%f / %f --> ", a1, b1);
Serial.print(a2);
Serial.print(" / ");
Serial.println(b2);
Generates the output:
982.661255 / 982.661000 --> 982.6612548828125 / 982.66100000000006
I expected the last output to be 982.661 or 982.661000 instead of 982.66100000000006.
