JSON to C++ Converter
Generate modern C++ structs from a JSON sample, using the standard library types you would write by hand.
Your data stays on your device
Input — JSON
- characters
- 0
- lines
- 0
- size
- 0 B
Output — C++
- characters
- 0
- lines
- 0
- size
- 0 B
Options
About this tool
Modelling JSON in C++ means choosing types: std::string for text, std::vector for arrays, and std::optional for values that may be absent. Getting the declaration order right also matters, since a struct must be defined before it is used as a member.
The generator emits nested structs first, in dependency order, so the file compiles as written. Optionally it adds nlohmann/json serialisation macros, which give you conversion in both directions with a single line per struct.
How to use this tool
- Paste your JSON sample.
- Set the root struct name.
- Choose whether to emit nlohmann/json macros and whether to use std::optional for nullable fields.
- Press Generate and copy the structs into a header file.
Key features
- std::string, std::vector and std::optional used idiomatically
- Nested structs emitted in dependency order so the file compiles top to bottom
- Optional NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE macros for serialisation
- int64_t and double distinguished from the sample
- C++ keywords and invalid identifiers renamed safely
- Optional include block for the standard headers used
Example
Input — JSON
{"count":12,"label":null}Output — C++
struct Root {
int64_t count;
std::optional<std::string> label;
};Good to know
- The standard library has no JSON support, so serialisation requires a third-party library such as nlohmann/json.
- Heterogeneous arrays cannot be typed and are reported rather than silently converted.
- std::optional requires C++17 or later.
Frequently asked questions
Which JSON library should I use?
nlohmann/json is the most common choice for its ergonomics. RapidJSON is significantly faster for large payloads but far more verbose to use.
Why is declaration order important?
C++ requires a complete type before it can be used as a member by value. The generator sorts structs so every dependency appears first.
std::optional or a default value?
std::optional when absence is meaningful and you want the compiler to force you to handle it. A default value is simpler but hides the distinction.
Is a header guard included?
A #pragma once is emitted when you enable the include block. Add a traditional guard if your project prefers one.
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