C++ ↔ Dart Type Translation

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

Further Reading

• Type Mapping
• Wire Protocol
• Pure C Bridge API