aJson.parse changing value of double

[merrillii]

I have a 5 digit precision double that I'm trying to parse and it seems to get munged by the parse method. The following test code shows the problem. The output will be:

Full string={"laserWavelen":638.12345}
Total json={"laserWavelen":638.12360}

The last two digits always seem to get screwed up. Any ideas how to fix this?

include

void setup() { // put your setup code here, to run once: Serial.begin(9600); }

void loop() { // put your main code here, to run repeatedly: char json_string[] = "{\"laserWavelen\":638.12345}\0";

aJsonObject* jsonObject = aJson.parse(json_string);

Serial.print("Full string="); Serial.println( json_string );

Serial.print("Total json="); char *p = aJson.print(jsonObject); if (p != NULL) { Serial.println(p); free(p); } else Serial.println("NULL!");

aJson.deleteItem(jsonObject);

delay(5000); }

[nw2s]

Doesn't Arduino only support single?

[merrillii]

You may be correct that I'm running out of bits. The arduino doc says 32 bits for a double. If I change the code to make the test number 0.12345 then it seems to work. So, any ideas for a workaround to getting a higher precision number through JSON?

[merrillii]

You are right that it's an Arduino precision issue. Even using string functions, the code fails:

float d = atof("638.12345"); char floatBuffer[20]; Serial.print("float test ="); dtostrf(d, 19, 10, floatBuffer); Serial.println(floatBuffer);

outputs: float test = 638.1234700000