[JNI] how to modify a java array in the C++ code ?

[yomgui]

in the java code :
byte [ ] aPictArrayUnpacked = new byte [ 3 ] ;

in the c++ code :
JNIEXPORT void JNICALL Java_tracker_UnpackPict (
JNIEnv * aEnv ,
jobject aObj ,
jbyteArray aPictArrayUnpacked )
{
jbyte * lBodyUnpacked = aEnv -> GetByteArrayElements (

aPictArrayUnpacked , 0 ) ;

memset ( lBodyUnpacked , 0 , 3 ) ;

aEnv -> ReleaseByteArrayElements (
aPictArrayUnpacked ,
lBodyUnpacked ,
0 ) ;
}

it crashes on the memset. what should I do ?

thanks
yomgui