Description

ARDUINOJSON_USE_DOUBLE determines the type used to store floating point values in JsonVariant:

  • If ARDUINOJSON_USE_DOUBLE == 0, then JsonVariant stores a float
  • If ARDUINOJSON_USE_DOUBLE == 1, then JsonVariant stores a double

The default is 0 on embedded systems, 1 otherwise.

Several .ino or .cpp files?

Be careful if several compilation units compose your program, i.e., if your project contains several .ino or .cpp files.

You should define the same value of ARDUINOJSON_USE_DOUBLE in each compilation unit; otherwise, the executable will be much bigger because it will contain two variants of the library.

Examples

Example with 32-bit precision

The following program uses 32-bit precision:

#define ARDUINOJSON_USE_DOUBLE 0
#include <ArduinoJson.h>

void example_float()
{
  StaticJsonDocument<200> doc;
  JsonObject root = doc.to<JsonObject>();
  root["pi"] = 3.14159265359;

  serializeJson(doc, Serial);
}

It produces the following output:

{"pi":3.141593}

See online demo on wandbox.org

Example with 64-bit precision

The following program uses 64-bit precision:

#define ARDUINOJSON_USE_DOUBLE 1
#include <ArduinoJson.h>

void example_double()
{
  StaticJsonDocument<200> doc;
  JsonObject root = doc.to<JsonObject>();
  root["pi"] = 3.14159265359;

  serializeJson(doc, Serial);
}

It produces the following output:

{"pi":3.141592654}

See online demo on wandbox.org

See also