When the JsonVariant points to an array, JsonVariant::add() appends a value to the array. Otherwise, this function does nothing.

In other words, JsonVariant::add() reproduces JsonArray::add().


bool add(bool value) const;

bool add(float value) const;
bool add(double value) const;

bool add(signed char value) const;
bool add(signed long value) const;
bool add(signed int value) const;
bool add(signed short value) const;
bool add(unsigned char value) const;
bool add(unsigned long value) const;
bool add(unsigned int value) const;
bool add(unsigned short value) const;

bool add(char *value) const;
bool add(const char *value) const;  // ⚠️ stores by pointer
bool add(const __FlashStringHelper *value) const;

bool add(const String &value) const;
bool add(const std::string &value) const;
bool add(const Printable& value);
bool add(std::string_view value);

bool add(JsonArray array) const;
bool add(JsonObject object) const;
bool add(JsonVariant variant) const;
bool add(const JsonDocument& doc) const;

bool add(TEnum value) const;  // alias of add(int)
bool add(T value) const;      // calls user-defined function

JsonArray add<JsonArray>() const;      // 🆕 adds a new empty array
JsonObject add<JsonObject>() const;    // 🆕 adds a new empty object
JsonVariant add<JsonVariant>() const;  // 🆕 adds a new null variant


value: the value to append to the array.

If you pass a JsonArray, a JsonObject, or a JsonVariant, JsonVariant::add() makes a complete clone of the argument. In other words, the value is stored by copy, not by reference.

As usual, ArduinoJson makes a copy of a string in the JsonDocument, except if it’s a const char*.

Return value

JsonVariant::add() returns a bool that tells whether the operation was successful or not:

  • true if the value was successfully added.
  • false if there was not enough memory in the JsonDocument.

String duplication

ArduinoJson makes a copy of the string when you call this function with one of the following types:

User-defined types

JsonVariant::add() supports user-defined types by calling convertToJson(). For example, to support tm, you must define:

bool convertToJson(const tm& src, JsonVariant dst) {
  char buf[32];
  strftime(buf, sizeof(buf), "%FT%TZ", &src);
  return dst.set(buf);

See also