How to handle variable number of arguments?

[arcticfox1919]

The C library function I want to bind has some variable number of parameters, ffigen doesn't seem to handle this situation very well, is there any way?

for example:

int func(int, ... ) {}

[dcharkes]

This is not yet supported in dart:ffi dart-lang/sdk#38578, so package:ffigen cannot generate something to support this yet.

[kingwill101]

@dcharkes any update on this, now that dart-lang/sdk#38578 has been completed?

[kingwill101]

I see that 79e845f was done but it seems to not work.

int fcntl (int __fd, int __cmd, ...);

  int fcntl(
    int __fd,
    int __cmd,
  ) {
    return _fcntl(
      __fd,
      __cmd,
    );
  }


  late final _fcntlPtr =
      _lookup<ffi.NativeFunction<ffi.Int Function(ffi.Int, ffi.Int)>>('fcntl');
  late final _fcntl = _fcntlPtr.asFunction<int Function(int, int)>();

[dcharkes]

If you write bindings yourself, you need to use VarArgs somewhere: https://api.dart.dev/stable/3.4.4/dart-ffi/VarArgs-class.html

If you want FFIgen to generate bindings, you need to configure FFIgen to do that.

functions:
  variadic-arguments:
    myfunc:
      // Native C types are supported
      - [int, unsigned char, long*, float**]
      // Common C typedefs (stddef.h) are supported too
      - [uint8_t, intptr_t, size_t, wchar_t*]
      // Structs/Unions/Typedefs from generated code or a library import can be referred too.
      - [MyStruct*, my_custom_lib.CustomUnion]

• Support variadic functions #497
• Support for generating Variadic functions dart-archive/ffigen#515

Since the feature is implemented, and was tracked by #497, I'll close this as duplicate issue.

Please file a new issue if you're having issues with VarArgs or FFIgen variadic-arguments.

[kingwill101]

@dcharkes is there a way to do variadic arguments that are functions? trying to generate libcurl bindings

CURL_EXTERN CURLcode curl_easy_setopt(CURL *curl, CURLoption option, ...);

and a version of the function accepts a

static size_t curl_callback(char *data, size_t size, size_t nmemb, void *clientp)

 functions:
    variadic-arguments:
      curl_easy_setopt:
        - [ 'long' ]
        - [ 'char*' ]
        - [ 'curl_off_t' ]
        - [ 'size_t curl_callback(char *data, size_t size, size_t nmemb, void *clientp)' ] <- this is what i want to somehow represent