Passing Structures

Question

How can I pass structures across C and Java, while calling native methods. e.g I've to pass myStruct from C to Java or vice versa
struct myStruct
long along;
char* astring;
short ashort;
is there any possible way of doin' it or Native Methods support only intrinsic data types as arguments (intrinsic data types like int, short etc etc).

Answer 1

Of course, there is a way. You should, however, decide on where to keep the main copy of your instance within C as struct or with an analogously constructed Java class.
If you choose to hold your main copy as C struct, you also have to define a Java class, which does not contain these fields but only wraps the C struct with appropriate getters and setters. These are native methods called by Java to access the struct members. One field is still required in your Java class, which somehow holds the native pointer to the struct of a particular instance. A long or int will do on most platforms.
The other approach is to hold all the data within the Java object. Only define native methods for operations you cannot perform in Java. Those native methods construct the C struct at runtime to pass this copy to the native functions that require it. If the native functions your are trying to call only take fields of this struct as arguments, the wrapping JNI method even becomes simpler. In any case, do not forget to copy modified values back into the Java instance.
http://java.sun.com/docs/books/tutorial/native1.1/index.html
http://java.sun.com/docs/books/tutorial/native1.1/implementing/field.html