C++ ↔ Dart Type Translation

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This page is a type translation cheat sheet: when you write a C++ API, you should know what type appears on the Dart side; when you call generated functions from Dart, you should also know what types C++ actually sends and receives. For the full rules, see Type Mapping and Wire Protocol.

C++ ↔ Dart Types

C++ Type	Dart Type	Encoding
`bool`	`bool`	1 byte (0/1)
`int8/16/32/64_t`	`int`	1/2/4/8 bytes LE
`uint8/16/32/64_t`	`int`	1/2/4/8 bytes LE
`float`	`double`	4 bytes IEEE 754
`double`	`double`	8 bytes IEEE 754
`std::string`	`String`	u32 length + UTF-8 bytes
`std::chrono::system_clock::time_point`	`DateTime`	i64 microseconds timestamp
`Int128` / `UInt128`	`BigInt`	length-prefixed decimal string

Containers

C++ Type	Dart Type	Encoding
`std::vector<uint8_t>`	`Uint8List`	u32 count + bytes
`std::vector<int32_t>`	`Int32List`	u32 count + elements
`std::vector<float>`	`Float32List`	u32 count + elements
`std::vector<double>`	`Float64List`	u32 count + elements
`std::vector<T>` (other)	`List<T>`	u32 count + N elements
`std::optional<T>`	`T?`	1 byte tag (0=None, 1=Some) + T
`std::unordered_map<K, V>`	`Map<K, V>`	u32 count + (K, V) pairs
`std::unordered_set<T>`	`Set<T>`	u32 count + N elements
`std::pair<T1, T2>`	`(T1, T2)`	encoded in order
`std::tuple<T1, T2, ...>`	`(T1, T2, ...)`	encoded in order

Enums

enum class BRIDGE_EXPORT OrderStatus : std::int32_t {
  kCreated = 0,
  kPaid = 1,
};

Must be marked with BRIDGE_EXPORT
Underlying type must be std::int32_t
Each constant must be explicitly assigned
Wire-encoded as int32

Data Classes

struct BRIDGE_DATA_CLASS Point {
  double x;
  double y;
};

Encoded field-by-field in declaration order
Field names are not transmitted
Inheritance, virtual functions, and methods are not supported

Opaque Classes

BRIDGE_OPAQUE objects are passed as handles on the wire, not field-by-field encoded.

Encoding Conventions

Little-endian: all multi-byte integers are little-endian
Order-sensitive: the Reader is a sequential cursor; read order must exactly match write order
Strings are not NUL-terminated: std::string transmits u32 length + bytes, without \0
No field names: data classes transfer values only, not field names

Error Frames

Payload of responseErr:

code    i32    currently always 0
message string error message