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Changes since 6.17.3

• Added support for custom converters (issue #687)
• Added support for Printable (issue #1444)
• Removed support for char values, see below (issue #1498)
• deserializeJson() leaves \uXXXX unchanged instead of returning NotSupported
• deserializeMsgPack() inserts null instead of returning NotSupported
• Removed DeserializationError::NotSupported
• Added JsonVariant::is<JsonArrayConst/JsonObjectConst>() (issue #1412)
• Added JsonVariant::is<JsonVariant/JsonVariantConst>() (issue #1412)
• Changed JsonVariantConst::is<JsonArray/JsonObject>() to return false (issue #1412)
• Simplified JsonVariant::as<T>() to always return T (see below)
• Updated folders list in .mbedignore (PR #1515 by @AGlass0fMilk)
• Fixed member-call-on-null-pointer in getMember() when array is empty
• serializeMsgPack(doc, buffer, size) doesn't add null-terminator anymore (issue #1545)
• serializeJson(doc, buffer, size) adds null-terminator only if there is enough room
• PlatformIO: set build.libArchive to false (PR #1550 by @askreet)

BREAKING CHANGES

Support for char removed

We cannot cast a JsonVariant to a char anymore, so the following will break:

char age = doc["age"];  //  error: no matching function for call to 'variantAs(VariantData*&)'

Instead, you must use another integral type, such as int8_t:

int8_t age = doc["age"];  // OK

Similarly, we cannot assign from a char anymore, so the following will break:

char age;
doc["age"] = age;  // error: no matching function for call to 'VariantRef::set(const char&)'

Instead, you must use another integral type, such as int8_t:

int8_t age;
doc["age"] = age;  // OK

A deprecation warning with the message "Support for char is deprecated, use int8_t or uint8_t instead" was added to allow a smooth transition.

as<T>() always returns T

Previously, JsonVariant::as<T>() could return a type different from T. The most common example is as<char*>() that returned a const char*. While this feature simplified a few use cases, it was confusing and complicated the implementation of custom converters.

Starting from this version, as<T> doesn't try to auto-correct the return type and always return T, which means that you cannot write this anymore:

Serial.println(doc["sensor"].as<char*>());  // error: invalid conversion from 'const char*' to 'char*' [-fpermissive]

Instead, you must write:

Serial.println(doc["sensor"].as<const char*>());  // OK

A deprecation warning with the message "Replace as<char*>() with as<const char*>()" was added to allow a smooth transition.

DeserializationError::NotSupported removed

On a different topic, DeserializationError::NotSupported has been removed. Instead of returning this error:

• deserializeJson() leaves \uXXXX unchanged (only when ARDUINOJSON_DECODE_UNICODE is 0)
• deserializeMsgPack() replaces unsupported values with nulls

Const-aware is<T>()

Lastly, a very minor change concerns JsonVariantConst::is<T>(). It used to return true for JsonArray and JsonOject, but now it returns false. Instead, you must use JsonArrayConst and JsonObjectConst.

View version history

How to install

There are several ways to install ArduinoJson, from simpler to more complex:

1. Use the Arduino Library Manager or equivalent
2. Download ArduinoJson-v6.18.0.h put it in your project folder
3. Download ArduinoJson-v6.18.0.zip and extract it into your libraries folder

Note: ArduinoJson-v6.18.0.h and ArduinoJson-v6.18.0.hpp are almost identical; the difference is that the .hpp keeps everything in the ArduinoJson namespace.

Try online

• JsonGeneratorExample
• JsonParserExample
• MsgPackParserExample