Passing pointers between C and Java through JNI

Question

I\'ve been storing c pointers in Java through JNI by following the advice of @tulskiy in this post Passing pointers between C and Java through JNI

The trick is to ca

Answer 1

There are various handy integer types in C. The one you want is probably intptr_t or uintptr_t:

return (jlong)(intptr_t) ptr;

The difference?

• Casting from intptr_t to jlong and back is guaranteed to work provided jlong is big enough (which you're implicitly assuming it is anyway).
• Casting from uinttptr_t to jlong and back avoids a sign-extension, but is undefined behaviour if the uintptr_t is too big to fit in a jlong (but all "sane" architectures/compilers just use two's complement arithmetic)

Answer 2

Try casting with intptr_t (store a pointer regardless of the platform capacity).