将jdouble转换为c类型的double

Question

如何将java类型变量的jdouble转换为c类型的double变量？

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.

Answer 2

No convertion is needed. I've used a simple static cast.

jfieldID varPtr = env->GetFieldID(dataClass, "var", "D");
jdouble jdoubleVar = env->GetDoubleField(dataClass, varPtr);

double varDouble = static_cast<double>(jdoubleVar);