如何用jna将byte []映射到void *缓冲区？

Question

I have the following C function:

    int read(int dev, void* buffer, unsigned int count)

This is usually call in C like:

    read(data->dev, data->buffer, 32000);

data is a struct, with the following:

    typedef struct {
         ssize_t dev; 
         char buffer[32000]; 
    } DATA;

And I have convert this to java, with jna with the following:

    public class Data{//not neccesary to extends of Structure, because is only used to package both variables together
          public int dev;
          public byte[] buffer;//in the constructor of the class set to 32000 elements
    }

   int read(int playdev, Buffer buffer, int count);

   //clib is the class to connect with  de C library

   ByteBuffer bf = ByteBuffer.wrap(data.buffer);
   clib.read(data.dev, bf , READ_SIZE);

And it gives me a "java.lang.Error: Invalid memory access" when I do the "clib.read"

Any idea how to go through this error???

I have tried to make a: int vox_playstr_read(int playdev, Pointer buffer, int count);

with

    ByteBuffer bf = ByteBuffer.wrap(data.buffer);
    Pointer pbuf = Native.getDirectBufferPointer(bf);
    clib.read(data.dev, pbuf, READ_SIZE);

and it gives me the same result.

Please, any ideas to make it work?

Answer 1

Try creating the ByteBuffer with ByteBuffer.allocateDirect and then use byteBuffer.put(..) if you want to set any initial data. Also, reset the position of the buffer, buffer.position(0).

ByteBuffer bb = ByteBuffer.allocateDirect(values.length);
bb.put(values);
bb.position(0);

Read Edwin's reply here for the reason to use allocateDirect.

Answer 2

technomage's comments to the original post are exactly right. Explicitly, on the Java side, declare your JNA interface method as you plan to use it:

int read(int playdev, byte[] buffer, int count);

clib.read(data.dev, data.buffer, READ_SIZE);

No need to use Buffer or ByteBuffer. Also, depending on whether the read function is exported __cdecl or __stdcall, your JNA interface should extends Library or extends StdCallLibrary respectively.