Converting a dart String to a pointer

[Chris Norman]

Hi all,

I'm currently writing bindings for a library. The header file contains the following definition:

SYZ_CAPI syz_ErrorCode syz_createBufferFromStream(syz_Handle *out, const char *protocol, const char *path, const char *options);

I've run the header file through ffigen, and is working well so far.

The resulting dart has the signature:

  int syz_createBufferFromStream(

    ffi.Pointer<ffi.Uint64> out,

    ffi.Pointer<ffi.Int8> protocol,

    ffi.Pointer<ffi.Int8> path,

    ffi.Pointer<ffi.Int8> options,

  ) {

    return _syz_createBufferFromStream(

      out,

      protocol,

      path,

      options,

    );

  }

First of all, is this right? I don't know enough C or C++ to know the difference, but the C++ method (the first code example) wants protocol, path and options given as const char * but the dart version is expecting Pointer<Int8>. Assuming that dart and ffigen know more about C++ than I do, how do I convert a normal string to this pointer type?

I thought the StringUtf8Pointer extension would help, but that returns a Pointer<Utf8>.

Any help would be greatly appreciated. Thanks in advance.

Take care,

Chris Norman

[Daco Harkes]

Hi Chris,

package:ffi Pointer<Utf8> is the answer indeed. You can use .cast<Utf8>() and .cast<Int8>() on Pointers to cast between different types of pointers. An example of these casts can be seen here [1].

Also see the ffigen documentation [2], and feel free to ask questions there or make suggestions. Prerak is very helpful!

[1] https://dart-review.googlesource.com/c/sdk/+/152141/10/samples/ffi/sqlite/lib/src/database.dart

[2] https://github.com/dart-lang/ffigen#how-does-ffigen-handle-c-strings

Kind regards,

 •  Daco Harkes
 •  Software Engineer
 •  dacoh...@google.com 
 •  🔵 Blue Dot Ally

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[Chris Norman]

That's great, thank you.

What threw me was the availability of dart:ffi, and the package of the same name.

Absolutely blew my tiny mind!

Take care,

Chris Norman

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