faq.md

FAQ

Can FFIgen be used for removing underscores or renaming declarations?

FFIgen supports regexp-based renaming. The regexp must be a full match. For renaming you can use regexp groups ($1 means group 1).

To renaming clang_dispose_string to string_dispose we can match it using clang_(.*)_(.*) and rename with $2_$1.

Here's an example of how to remove prefix underscores from any struct and its members.

structs:
  ...
  rename:
    '_(.*)': '$1' # Removes prefix underscores from all structures.
  member-rename:
    '.*': # Matches any struct.
      '_(.*)': '$1' # Removes prefix underscores from members.

How to generate declarations only from particular headers?

The default behavior is to include everything directly/transitively under each of the entry-points specified.

If you only want to have declarations directly particular header you can do so using include-directives. You can use glob matching to match header paths.

headers:
  entry-points:
    - 'path/to/my_header.h'
  include-directives:
    - '**my_header.h' # This glob pattern matches the header path.

Can FFIgen filter declarations by name?

FFIgen supports including/excluding declarations using full regexp matching.

Here's an example to filter functions using names:

functions:
  include:
    - 'clang.*' # Include all functions starting with clang.
  exclude:
    - '.*dispose': # Exclude all functions ending with dispose.

This will include clang_help. But will exclude clang_dispose.

Note: exclude overrides include.

How does FFIgen handle C Strings?

FFIgen treats char* just as any other pointer (Pointer<Int8>). To convert these to/from String, you can use package:ffi. Use ptr.cast<Utf8>().toDartString() to convert char* to dart string and "str".toNativeUtf8() to convert string to char*.

How are unnamed enums handled?

Unnamed enums are handled separately, under the key unnamed-enums, and are generated as top level constants.

Here's an example that shows how to include/exclude/rename unnamed enums:

unnamed-enums:
  include:
    - 'CX_.*'
  exclude:
    - '.*Flag'
  rename:
    'CXType_(.*)': '$1'

How can I handle unexpected enum values?

Native enums are, by default, generated into Dart enums with int get value and fromValue(int). This works well in the case that your enums values are known in advance and not going to change, and in return, you get the full benefits of Dart enums like exhaustiveness checking.

However, if a native library adds another possible enum value after you generate your bindings, and this new value is passed to your Dart code, this will result in an ArgumentError at runtime. To fix this, you can regenerate the bindings on the new header file, but if you wish to avoid this issue entirely, you can tell FFIgen to generate plain Dart integers for your enum instead. To do this, simply list your enum's name in the as-int section of your FFIgen config:

enums:
  as-int:
    include:
      - MyIntegerEnum
      - '*IntegerEnum'
    exclude:
      - FakeIntegerEnum

Functions that accept or return these enums will now accept or return integers instead, and it will be up to your code to map integer values to behavior and handle invalid values. But your code will be future-proof against new additions to the enums.

Why are some struct/union declarations generated even after excluded them in config?

This happens when an excluded struct/union is a dependency to some included declaration. (A dependency means a struct is being passed/returned by a function or is member of another struct in some way.)

Note: If you supply structs.dependency-only as opaque FFIgen will generate these struct dependencies as Opaque if they were only passed by reference (pointer).

structs:
  dependency-only: opaque
unions:
  dependency-only: opaque

How to expose the native pointers?

By default, the native pointers are private, but you can use the symbol-address subkey for functions/globals and make them public by matching with its name. The pointers are then accessible via nativeLibrary.addresses.

Example:

functions:
  symbol-address:
    include:
      - 'myFunc' # Match function name.
      - '.*' # Do this to expose all function pointers.
    exclude: # If you only use exclude, then everything not excluded is generated.
      - 'dispose'

How to get typedefs to Native and Dart type of a function?

By default, these types are inline. But you can use the expose-typedef subkey for functions to generate them. This will expose the Native and Dart type. E.g. for a function named hello the generated typedefs are named as NativeHello and DartHello.

Example:

functions:
  expose-typedefs:
    include:
      - 'myFunc' # Match function name.
      - '.*' # Do this to expose types for all functions.
    exclude: # If you only use exclude, then everything not excluded is generated.
      - 'dispose'

How are Structs/Unions/Enums that are referred to via typedefs handled?

Named declarations use their own names even when inside another typedef. However, unnamed declarations inside typedefs take the name of the first typedef that refers to them.

Why are some typedefs not generated?

The following typedefs are not generated:

• They are not referred to anywhere in the included declarations.
• They refer to a struct/union having the same name as itself.
• They refer to a boolean, enum, inline array, Handle or any unsupported type.

How are macros handled?

FFIgen uses clang's own compiler frontend to parse and traverse the C header files. FFIgen expands the macros using clang's macro expansion and then traverses the expanded code. To do this, FFIgen generates temporary files in a system tmp directory.

A custom temporary directory can be specified by setting the TEST_TMPDIR environment variable.

What are these logs generated by FFIgen and how to fix them?

FFIgen can sometimes generate a lot of logs, especially when it's parsing a lot of code.

• SEVERE logs are something you definitely need to address. They can be caused due to syntax errors, or more generally missing header files (which need to be specified using compiler-opts in config).
• WARNING logs are something you can ignore, but should probably look into. These are mostly indications of declarations FFIgen couldn't generate due to limitations of dart:ffi, private declarations (which can be resolved by renaming them via FFIgen's config) or other minor issues in the config file itself.
• Everything else can be safely ignored. Its purpose is to simply let you know what FFIgen is doing.
• The verbosity of the logs can be changed by adding a flag with the log level, e.g. dart run ffigen --verbose <level>. Level options are [all, fine, info (default), warning, severe]. The all and fine will print a ton of logs are meant for debugging purposes only.

How can type definitions be shared?

FFIgen can share type definitions using symbol files.

• A package can generate a symbol file using the output.symbol-file config.
• And another package can then import this, using import.symbol-files config.
• Doing so will reuse all the types such as Struct/Unions, and will automatically exclude generating other types (E.g. functions, enums, macros).

Checkout examples/shared_bindings for details.

For manually reusing definitions from another package, the library-imports and type-map config can be used.