JSON to C++ Struct Generator

Generate C++ types from JSON

C++ has no built-in reflection, so mapping JSON onto your own types normally means writing a struct and then a pair of serialization functions for every object in the payload. This JSON to C++ converter generates both from a sample. Each JSON object becomes a struct (or a class with getters and setters), keys become snake_case members, nested objects become their own types, arrays become std::vector<T>, integers become int64_t, fractional numbers become double, and fields that are missing or null in part of the sample become std::optional<T>. Everything is wrapped in the namespace you choose and emitted as a single header guarded by #pragma once.

Type inference is done by quicktype, which merges all elements of each array before choosing a type. A field that appears in only some items is still captured as optional, so parsing the full response does not throw on a missing key.

nlohmann/json integration

The generated header is designed for nlohmann/json, the most popular JSON library for modern C++. For every type it defines from_json and to_json overloads that map members back to the original JSON keys, plus small helpers for optional values. Once json.hpp is available, reading a document is a single call to nlohmann::json::parse(text).get<Root>(), and writing it back is nlohmann::json j = value;. Tick Types only if you only need the declarations — for example to use with a different serializer — and Use Boost if your toolchain cannot use C++17.

Tips for production code

Paste a complete sample with several array items and optional fields filled in so the types are accurate. Empty arrays and nulls fall back to nlohmann::json, which you will usually want to replace. Rename the root type to match your domain, set a namespace that fits your project, and run clang-format on the result. Review integer widths, consider enum class for strings with a fixed set of values, and note that date-time strings stay std::string so you can parse them with the library of your choice. All processing happens locally, so internal payloads stay on your machine.