JsonDocument::operator[]
Description
JsonDocument::operator[] gets, replaces, or adds a value in the JsonDocument.
Depending on the argument type the JsonDocument can be used like a JsonArray or a JsonObject.
If you use this operator to set a value in an empty JsonDocument, it automatically converts JsonDocument to the appropriate type. This feature allows creating object without calling JsonDocument::to<JsonObject>(). Here is an example:
StaticJsonDocument<256> doc;
doc["wifi"]["SSID"] = "TheBatCave";
The two lines above create the following document:
{
"wifi": {
"SSID": "TheBatCave"
}
}
All types are stored by copy, except const char* which is stored by pointer.
If you need to know if the insertion succeed, use JsonVariant::set() instead.
Signatures
// mimics a JsonArray
ElementProxy operator[](size_t index);
// mimics a JsonObject
MemberProxy operator[](const char* key); // ⚠️ stores key as a pointer
MemberProxy operator[](char* key);
MemberProxy operator[](const String& key);
MemberProxy operator[](const std::string& key);
MemberProxy operator[](const __FlashStringHelper* key);
MemberProxy operator[](std::string_view key);
You can also call JsonDocument::operator[] on a constant JsonDocument, but the return type will be a JsonVariantConst, a read-only version of JsonVariant.
Arguments
index: the index in the JsonArray.
key: the key in the JsonObject
Return value
A proxy class that allows using the JsonDocument as an array or a dictionary. If this concept of proxy class is unfamiliar to you, just think of a JsonVariant instead.
Please see JsonArray::operator[] and JsonObject::operator[] for explanations about ElementProxy and MemberProxy.
Example
DynamicJsonDocument doc(1024);
deserializeJson(doc, "{\"hello\":\"world\"}");
const char* hello = variant["hello"];
deserializeJson(doc, "[\"hello\",\"world\"]");
const char* world = variant[1];