JsonVariantConst::as<T>()
Description
JsonVariantConst::as<T>()
casts the value pointed by the JsonVariantConst
to the specified type.
Signatures
bool as<bool>() const;
float as<float>() const;
double as<double>() const;
signed char as<signed char>() const;
unsigned char as<unsigned char>() const;
signed int as<signed int>() const;
unsigned int as<unsigned int>() const;
signed short as<signed short>() const;
unsigned short as<unsigned short>() const;
signed long as<signed long>() const;
unsigned long as<unsigned long>() const;
unsigned long long as<unsigned long long>() const; // ⚠️ may require ARDUINOJSON_USE_LONG_LONG
signed long long as<signed long long>() const; // ⚠️ may require ARDUINOJSON_USE_LONG_LONG
signed __int64 as<signed __int64>() const; // ⚠️ may require ARDUINOJSON_USE_INT64
unsigned __int64 as<unsigned __int64>() const; // ⚠️ may require ARDUINOJSON_USE_INT64
const char* as<char*>() const; // ⛔ removed in 6.20
const char* as<const char*>() const;
String as<String>() const;
std::string as<std::string>() const;
JsonArray as<JsonArray>() const; // ⚠️ always returns null
JsonObject as<JsonObject>() const; // ⚠️ always returns null
JsonVariant as<JsonVariant>() const; // ⚠️ always returns null
JsonArrayConst as<JsonArrayConst>() const;
JsonObjectConst as<JsonObjectConst>() const;
JsonVariantConst as<JsonVariantConst>() const;
TEnum as<TEnum>() const; // 🆕 alias of as<int>() (added in 6.15.2)
T as<T>() const; // 🆕 calls user-defined converter (added in 6.18.0)
Return value
JsonVariantConst::as<T>()
returns the value pointed by the JsonVariantConst
casted to the specified type.
This function returns a default value if the cast is not possible. The default value is:
0
for numerical typesNULL
forconst char*
- A null reference for
JsonArray
andJsonObject
.
If you want to change the default value, you need to use JsonVariantConst::operator|
instead.
Integer overflows
JsonVariantConst::as<T>()
is aware of integer overflows and only returns a value if it can fit in the specified type.
For example, if the value contains 512
, as<char>()
returns 0
, but as<int>()
returns 512
.
This feature was added in ArduinoJson 6.10.0
User-defined types 🆕
JsonVariantConst::as<T>()
supports user-defined types by calling convertFromJson()
.
For example, to support tm
, you must define:
void convertFromJson(JsonVariantConst src, tm& dst) {
strptime(src.as<const char*>(), "%FT%TZ", &dst);
}
This feature was added in ArduinoJson 6.18.0, see article for details.
Example
StaticJsonDocument<256> doc;
deserializeJson(doc, "{\"answer\":42}");
JsonVariantConst answer = doc["answer"];
int i = answer.as<int>(); // <- i == 42
double d = answer.as<double>(); // <- d == 42.0
const char* s = answer.as<const char*>(); // <- s == NULL