Re: Array of a simple structure in JNA api

[Tobias Wolf]

My Memory dump look like that:

 

OaIdl$SAFEARRAYBOUND(auto-allocated@0xf41290 (16 bytes)) {

WinDef$ULONG cElements@0=10

WinDef$LONG lLbound@8=0

}

memory dump

[0a000000]

[00000000]

[00000000]

[00000000]

 

I changed the class like that to be absolutely conform to the MS api:

 public static class SAFEARRAYBOUND extends Structure {
  public static class ByReference extends SAFEARRAYBOUND implements
    Structure.ByReference {
  }

  public ULONG cElements;

  public LONG lLbound;

  public SAFEARRAYBOUND() {
  }

  public SAFEARRAYBOUND(Pointer pointer) {
   super(pointer);
   this.read();
  }

  public SAFEARRAYBOUND(int cElements, int lLbound) {
   this.cElements = new ULONG(cElements);
   this.lLbound = new LONG(lLbound);
   this.write();
  }

  @Override
  protected List getFieldOrder() {
   return Arrays.asList(new String[] { "cElements", "lLbound" });
  }
 }

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On Wednesday, January 16, 2013 11:33:21 AM UTC+1, Tobias Wolf wrote:

How are arrays of structures handled by JNA api?

For example I have:

        SAFEARRAYBOUND[] rgsabound = new SAFEARRAYBOUND[1];
        rgsabound[0] = new SAFEARRAYBOUND(size, 0);

and when I take a look to the backing memory then I see that it is not being written to memory. Please explain why!
Which methods of the Structure class needs to be overwritten to solved that?


below is the code of the structure:
    public static class SAFEARRAYBOUND extends Structure {

        public static class ByReference extends SAFEARRAYBOUND implements
                Structure.ByReference {
        }

        public int cElements;

        public int lLbound;

        public SAFEARRAYBOUND() {
        }

        public SAFEARRAYBOUND(int cElements, int lLbound) {
            this.cElements = cElements;
            this.lLbound = lLbound;
        }

        public SAFEARRAYBOUND(Pointer pointer) {
            super(pointer);
        }

        @Override
        protected List getFieldOrder() {
            return Arrays.asList(new String[] { "cElements", "lLbound" });
        }
    }

[Timothy Wall]

What are you trying to achieve? It's been a long time since I dealt with COM.

The only special handling of arrays of structures that JNA provides is with Structure.toArray(), which allocates a large block of memory to represent a contiguous array of native struct (which usually are indistinguishable from a simple "struct *").

Pointer[] and PointerType[] have temporary memory allocated to hold arrays of native pointers; use these when dealing with arrays of pointer to struct (usually represented by "struct**" in native code).

[Timothy Wall]

Your type sizing seems off. The structure should only be 8 bytes (4 bytes for each field), unless for whatever reason you're running on something other than Windows.

LONG on windows is 32 bits on both 32- and 64-bit versions.

[Tobias Wolf]

You`re joking?! I`m on Windows 8 32bit.

[Timothy Wall]

hm... maybe that's part of the problem. maybe JNA is not detecting that windows 8 is windows --- what does the VM report for "os.name"?

[Tobias Wolf]

ehhhh, no it was my fault, I made a wrong data type definition.
But I can check the jna os detetion mode, please give me a pointer in which class I`ve to look for. Is JNA overwriting the os.name property?

[Timothy Wall]

Platform.isWindows()

JNA simply looks at os.name system property.

[Tobias Wolf]

the property name.os gives "Windows 8", JNA works correct