How can i send pointer to struct from java to c?

Question

Hi
my native function expect to get pointer to struct as follow:
int sendTo(const struct sockaddr_in *lpTo)
when the c function prototype is as follow:
JNIEXPORT jint JNICALL Java_myProg_sr_SendTo(JNIEnv env, jobject sockaddr_in lpTo)
my question is :
should i send the native function jobject as i did and then create a new instance of (struct sockaddr_in *) in the native function and that initialize all struct fields from the jobject (java object wrapper) fileds ,
or
should i just send jlong value that i stored in my java program and that points to the (struct sockaddr_in *) address after casting to this type???

Answer 1

You are going to need to create a new instance of sockaddr_in and populate it's fields from the Java object. This is the safest thing to do. I haven't seen anywhere in the documentation that you can simply cast objects to C structs, only primitive values.
For more info on populating fields, try:
http://java.sun.com/docs/books/tutorial/native1.1/implementing/field.html
http://java.sun.com/products/jdk/1.1/docs/guide/jni/spec/functions.doc.html#16536