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Showing content from https://arduinojson.org/v5/api/jsonbuffer/parseobject/ below:

JsonBuffer::parseObject() | ArduinoJson 5

Description

Allocates and populate a JsonObject from a JSON string.

By design, the parser needs to alter the string to insert null-terminators and replace escaped chars. If the JSON string is read-only, it will have to duplicate the input string, this consume more space in the JsonBuffer. Therefore, it’s recommended to have a JSON input in a char[] or a char*.

Signatures

// The first overload, which accepts a modifiable array of chars, is the most efficient
// since it allows the zero-copy feature.
JsonObject& parseObject(char* json, uint8_t nestingLimit=10);

// The following overloads, which accept read-only strings, require a bigger JsonBuffer
// because parts of the JSON input has to be copied.
JsonObject& parseObject(const char* json, uint8_t nestingLimit=10);
JsonObject& parseObject(const String& json, uint8_t nestingLimit=10);
JsonObject& parseObject(const std::string& json, uint8_t nestingLimit=10);
JsonObject& parseObject(const __FlashStringHelper* json, uint8_t nestingLimit=10);

// The two last overloads, which accept input streams, make copy of the input too.
JsonObject& parseObject(Stream& json, uint8_t nestingLimit=10);
JsonObject& parseObject(std::istream& json, uint8_t nestingLimit=10);

Arguments

json is the input string to be parsed.

nestingLimit specifies the maximum level of nesting allowed in the JSON string. If set to 0, only a flat object can be parsed. If set to 1, the object can contain nested objects or objects but only 1 level deep. And bigger values will allow more level of nesting. The purpose of this feature is to prevent stack overflow that could lead to a security risk.

Return value

Returns a reference to the new JsonObject or JsonObject::invalid() if the allocation fails.

How to view the JSON input?

When you pass a Stream to JsonBuffer::parseObject(), it consumes the input but doesn’t print anything to the serial port, which makes troubleshooting difficult.

If you want to see what JsonBuffer::parseObject() consumed, use ReadLoggingStream from the StreamUtils library.

Performance

When you pass a Stream to JsonBuffer::parseObject(), it consumes bytes one by one, which can be slow depending on the input you use. For example, if you read from a SPIFFS file, you can read twenty times faster by reading chunks of 64 bytes.

To read the stream in chunks, you can use ReadBufferingStream from the StreamUtils library.

Example

char json[] = "{\"hello\":\"world\"}";
StaticJsonBuffer<200> jsonBuffer;
JsonObject& object = jsonBuffer.parseObject(json);
const char* world = object["hello"];