ArduinoJson 5.13.0 is out!

Firmware Libraries
1

I just released a new version of ArduinoJson, a library to serialize and deserialize JSON documents.

Let’s see what’s new.

New rules for string duplications

When a program adds a string, ArduinoJson stores it differently depending on the type of the string.

In previous versions, ArduinoJson stored a pointer when the string was a plain old C string (char*, const char*, char[]), but stored a copy when the string had any other type (String, Flash strings…).

ArduinoJson 5.13 changes the rules: now, only const char* is stored with a pointer, all other string types are duplicated, which greatly simplifies our programs.

Example

Since older versions stored char[] strings with a pointer, we used to see curious behavior when adding strings in a loop. To prevent ArduinoJson for storing the same pointer (an thus the same string) several times, we had to call JsonBuffer::strdup():

JsonArray& array = jsonBuffer.createArray();
for (int i=0; i<3; i++) {
    char buffer[16];
    sprintf(buffer, "iteration %d", 0);
    array.add(jsonBuffer.strdup(buffer)); // <- need to duplicate :-(
}
array.printTo(Serial);

Thanks to the implicit duplication of char*, we can simplify this program to:

JsonArray& array = jsonBuffer.createArray();
for (int i=0; i<3; i++) {
    char buffer[16];
    sprintf(buffer, "iteration %d", 0);
    array.add(buffer); // <- implicit duplication :-)
}
array.printTo(Serial);

Improvements to RawJson()

RawJson() is a special function to insert raw JSON fragments in a JsonArray or a JsonObject.

In previous versions, RawJson() only accepted const char* as an argument; now, in ArduinoJson 5.13, it also accepts String objects and Flash strings too.

But there is more: strings marked with RawJson() obey to the same duplication rules as other strings.

Here is an example:

JsonObject& root = jsonBuffer.createObject();
root["coord"] = RawJson(F("{\"lat\":48.74801,\"lon\":2.293491}"));

Bye bye strdup()

The new rules for string duplication make JsonBuffer::strdup() useless.

In ArduinoJson 5.13, JsonBuffer::strdup() is flagged as deprecated, so you’ll have a compilation warning if your program uses it.

I’ll probably remove the function in a future release, so I encourage you to update your programs.

Link to the full article

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Thanks for the hard work!