converting jdouble to double of type c

Question

How can i convert jdouble of java type variable to double variable of type c ?

Answer 1

You don't have to, it's just a typedef like so:

typedef double jdouble;

So no conversion is needed, once you have a jdouble you can treat it just as a double.

See for instance this code example from Standford:

JNIEXPORT jdouble JNICALL Java_Summer_sum__DD
(JNIEnv *env, jobject jobj, jdouble j1, jdouble j2) {
    return j1 + j2;
}

The addition is done directly with the jdouble values, trusting the compiler to figure out how to generate the required code.