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3 messages in net.java.dev.jna.usersRe: [jna-users] passing in a struct c...| From | Sent On | Attachments |
|---|---|---|
| bb...@cox.net | Jul 10, 2007 11:19 am | |
| Timothy Wall | Jul 10, 2007 5:10 pm | |
| bb...@cox.net | Jul 11, 2007 5:50 am |
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| Subject: | Re: [jna-users] passing in a struct containing a null pointer? | Actions... |
|---|---|---|
| From: | bb...@cox.net (bb...@cox.net) | |
| Date: | Jul 11, 2007 5:50:12 am | |
| List: | net.java.dev.jna.users | |
Okay, thanks, I'd missed the Memory class, and without knowing about it was not
seeing how to allocate things before the call. So this C code
struct CS {
unsigned char *bPointer;
long *iPointer;
}
struct CS cs;
cs.bPointer = new unsigned char[len];
cs.bPointer[0] = '\0';
cs.iPointer = 0;
int rv = f(cs);
might become this Java
public class S extends Structure {
public Pointer bPointer;
public Pointer iPointer;
public S(int len) {
s.bPointer = new Memory(len);
s.iPointer .???(null); // Do I just leave IPointer alone? Or...?
allocateMemory(); // Am I letting it calculate the size, or do
I
// have to say
"allocateMemory(8);" to make
// an S be big enough for
two pointers?
}
}
S s = new S(len);
I could not find any setByteArray(), so I assume you meant something like the
following
to let the caller give meaningful values to allocated memory before the call to
f():
b = s.bPointer.getByteArray(0,len);
b[0] = '\0';
int rv = lib.INSTANCE.f(s);
- Ben ---- Timothy Wall <twal...@dev.java.net> wrote:
On Jul 10, 2007, at 2:19 PM, <bb...@cox.net> <bb...@cox.net> wrote:
I'm having trouble passing a struct to a library function.
The C declaration for S is: struct CS { unsigned char *barray; long *iarray; }
This is a structure containing two pointers, not two arrays. Java arrays are always interpreted as being inline in the structure, so if you want a pointer, use a Pointer. Structure doesn't currently support ByteBuffer as a structure member, so you'll need to create a Memory object of the appropriate size and call setByteArray on it for the first field and use a null value for the second.
I need (at least for now) to be able to write Java that looks like the following C code, with f() being in a .dll library:
struct CS cs; cs.barray = new unsigned char[len]; cs.iarray = 0; int rv = f(cs);
I have code that looks like the following, and it is failing. During invocation the field s.memory is still null, causing an exception. What am I doing wrong? (I hope that during simplification of my code to get the snippet below, I didn't discard the problem...) I think the problem is not barray, but rather iarray. How do I set it null?
public class S extends Structure { public byte[] barray; public int[] iarray; public S(byte []obs) { barray = obs; iarray = null; } }
In structures where fields must be initialized, you must explicitly call allocateMemory() after initialization is complete.