Question 1

nlohmann/json vs RapidJSON which is better?

Accepted Answer

nlohmann/json excels in ease of use and integration with a clean, STL-like API, while RapidJSON is optimized for performance and memory efficiency. Choose based on whether developer productivity or raw speed is your priority.

Question 2

How to serialize a custom class to JSON with nlohmann/json?

Accepted Answer

Define to_json and from_json functions in your class's namespace, or use convenience macros like NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE. The library handles conversions automatically, as detailed in the 'Arbitrary Types Conversions' section.

Question 3

Is nlohmann/json thread-safe?

Accepted Answer

The library doesn't guarantee thread safety for concurrent modifications to the same JSON object, as typical with STL containers. You need external synchronization for multi-threaded access, similar to standard C++ data structures.

Question 4

How to parse JSON from a string in C++ using nlohmann/json?

Accepted Answer

Use json::parse() with a string literal or std::string, or append _json to a string literal with the nlohmann::literals namespace. Examples show both methods, including error handling for malformed input.

Question 5

Does nlohmann/json support JSON Schema validation?

Accepted Answer

No, the library focuses on parsing, serialization, and manipulation (e.g., JSON Patch), but doesn't include built-in JSON Schema validation. You'd need to implement validation separately or use another library.

Question 6

How to handle large JSON files with nlohmann/json?

Accepted Answer

For memory efficiency, use the SAX interface (sax_parse) for event-driven parsing instead of loading the entire DOM. The README explains SAX usage, which avoids constructing full JSON objects in memory.

JSON for Modern C++

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