How to know the type of a value?
JsonVariant, which is the type that hold the values in JsonArray and JsonObject, provides the method is<T>() that returns true if the value is of type T.
Type of a value in an object
object["key"] = "value";
object["key"].is<const char*>(); // true
object["key"].is<int>(); // false
object["key"].is<JsonObject&>(); // false
Type of a value in an array
array.add(42);
array[0].is<const char*>(); // false
array[0].is<int>(); // true
array[0].is<JsonObject&>(); // false
In object iteration loop
To get the type of a value while iterating an object:
for (auto kvp : object) {
const char* key = kvp.key;
if (kvp.value.is<int>()) {
int value = kvp.value.as<int>();
// ...
} else if (kvp.value.is<char*>()) {
const char* value = kvp.value.as<char*>();
// ...
} else {
// ...
}
}for (JsonObject::iterator it=object.begin(); it!=object.end(); ++it) {
const char* key = it->key;
if (it->value.is<int>()) {
int value = it->value.as<int>();
// ...
} else if (value.is<char*>()) {
const char* value = it->value.as<char*>();
// ...
} else {
// ...
}
}In array iteration loop
for (auto value : array) {
if (value.is<int>()) {
int value = value.as<int>();
// ...
} else if (value.is<char*>()) {
const char* value = value.as<char*>();
// ...
} else {
// ...
}
}for (JsonArray::iterator it=array.begin(); it!=array.end(); ++it) {
if (it->is<int>()) {
int value = it->as<int>();
// ...
} else if (it->is<char*>()) {
const char* value = it->as<char*>();
// ...
} else {
// ...
}
}See also
In the “Case Studies” chapter of Mastering ArduinoJson, there is a complete example that shows how to display the type and value of all the members of an object, and of all its children recursively.
