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    <p>First of all JNA handle automatically it's own memory allocations which means that to following line is useless (and can damage the memory stack) :</p> <pre><code>myPointer.clear(size); //is this required to clear the memory and release the Pointer to the GC?? </code></pre> <p>Next it also automatically deal with native pointer types which means that both lines below are equivalent in your case :</p> <pre><code>public int myCfunc(Pointer s, IntByReference ls); public int myCfunc(myClass s, IntByReference ls); </code></pre> <p>and thus JNA will do <code>myObj.write();</code> and <code>read</code> for you.</p> <p>The following is 100% correct but I suggest that you log <code>len.getValue()</code> before and after your call to <code>myCfunc</code> (which sould give 3*4=12 ; 3 int of 4 bytes) : </p> <pre><code>int size = Native.getNativeSize(myClass.class); IntByReference len = new IntByReference(size); </code></pre> <p>If all of this is correct then you probably have an error in your structure's prototype.</p> <p>From my experience this is mostly due to an outdated C header file or an outdated library : </p> <ul> <li>You are using header version 2.0 which states that struct's values are int but your linking against library v1.0 which takes a bytes structure</li> <li>You are using header version 2.0 which states that struct's values are int but your linking against library v1.9 which takes two ints and a byte</li> </ul> <p>in the end your code should look like this :</p> <pre><code>public void foo(){ myWrapper wrapper = (myWrapper) Native.loadLibrary("SomeDllWithLegacyCode", myWrapper.class); myClass myObj = new myClass(); myObj.x = 1; myObj.y = 2; int size = Native.getNativeSize(myClass.class); IntByReference len = new IntByReference(size); //log len.getValue wrapper.myCfunc(myObj, len); //log len.getValue } </code></pre> <p>You can also try to <em>voluntarily</em> decrease len's value for debugging purposes eg :</p> <pre><code>IntByReference len = new IntByReference(size-1); IntByReference len = new IntByReference(size-2); IntByReference len = new IntByReference(size-3); //... IntByReference len = new IntByReference(size-11); </code></pre> <p>This won't do what you wan't but at least it should give you the correct "max len"</p>
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