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6 messages in net.java.dev.jna.usersRe: [jna-users] how to set a pointer| From | Sent On | Attachments |
|---|---|---|
| Glick, Gene (GE Indust, Security) | Sep 19, 2007 2:02 pm | |
| Timothy Wall | Sep 19, 2007 2:55 pm | |
| Glick, Gene (GE Indust, Security) | Sep 20, 2007 9:00 am | |
| Albert Strasheim | Sep 20, 2007 9:23 am | |
| Timothy Wall | Sep 20, 2007 9:30 am | |
| Glick, Gene (GE Indust, Security) | Sep 20, 2007 11:23 am |
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| Subject: | Re: [jna-users] how to set a pointer | Actions... |
|---|---|---|
| From: | Timothy Wall (twal...@dev.java.net) | |
| Date: | Sep 20, 2007 9:30:15 am | |
| List: | net.java.dev.jna.users | |
On Sep 20, 2007, at 12:01 PM, Glick, Gene (GE Indust, Security) wrote:
I'm confused. ByteBuffer is an abstract class. To use it means writing all its methods first, right? Seems like a lot of work.
Look at ByteBuffer.wrap (a static method). You don't have to implement anything; the class provides you with an instantiation. The JNA native layer can use Buffer interchangeably with native pointers.
Let me be a little more specific in what I'm trying to do:
1. In some java code, I have created a 'byte[] buf' of data. 2. In some c shared library (.dll) the method is looking for a passed parameter of 'uint8_t *buf' 3. The jna header file (not written by me, but could be modified if need be) is looking for type 'Pointer buf'.
in C it goes something like this: a) byte buf[10]; b) byte *ptrBuf; c) ptrBuf = &buf[0]; d) someMethod(uint8_t *ptrBuf); in Java, using the JNA it goes something like this: a) byte [] buf = new byte[10]; b) Pointer ptrBuf = new Pointer(); c) *** here's where I am lost *** d) someInstance.someMethod(Pointer ptrBuf);
So, how to get the Pointer to be set to &buf[0]?
Since your C method is expecting a pointer to uint8_t, you can safely declare the argument on the Java side as "byte[]". No conversion necessary. I'd recommend changing the Java interface definition to be more precise.
If your C program expects a pointer or array of a specific type, then you should use a Java array of the matching type in the interface method definition.
char* = byte[] short* = short[] int* = int[] etc.
If your C program expects a block of memory that might have different representations, then "Buffer" is more appropriate. Java provides "wrap" methods on ByteBuffer, ShortBuffer, IntBuffer, et al. which can wrap a java primitive array, and JNA will interpret the argument as a pointer to the data wrapped.
With primitive arrays, Buffers, Structures/Unions, PointerType, et al., there's little reason to use Pointer as an argument type except as a placeholder (usually where "void*" is used as an opaque handle).