An efficient way to convert ByteData in Dart to unsigned char* in C++?

Question

I'm doing it in this way:

Pointer<Uint8> _byteDataToPointer(ByteData byteData) {
  final uint8List = byteData.buffer.asUint8List();
  final length = uint8List.lengthInBytes;
  final result = allocate<Uint8>(count: length);

  for (var i = 0; i < length; ++i) {
    result[i] = uint8List[i];
  }

  return result;
}

Is there a more efficient way like JNIEnv::GetByteArrayRegion in JNI?

Thank you very much!

score 3 · Accepted Answer · answered Dec 20 '19 at 11:20

3

This is always going to involve a copy, so is there something more efficient than your for loop? Maybe.

After allocating your Uint8Pointer use asTypedList to convert it to a Uint8List. Now you have access to its copy primitive like setAll and setRange to copy from the source to the destination.

What's the original source of the ByteData? If you knew the size in advance, could you allocate the Uint8Pointer first, convert to typed data and then read directly into that?

answered Dec 20 '19 at 11:20

Richard Heap

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Thank you~! `asTypedList` is what I need! – LvSheng Dec 20 '19 at 12:23
and the original source of the `ByteData` is `rootBundle.load`, I don't find a way to read directly into my Uint8List – LvSheng Dec 20 '19 at 12:34

An efficient way to convert ByteData in Dart to unsigned char* in C++?

1 Answers1