JNI: converting jbyteArray to const unsigned char*

This should help you. It allows a c unsigned char array to be set from Java. It uses a jshortArray instead of a jbyteArray as you can't get the full 8 bit positive number range of an unsigned char from a java byte (128 - 255 not possible). Change occurrences of byte to short if that is what you really want.

Java class:

public class example {

public final static native void set_Foo_array(long jarg0, short[] jarg1);

public final static native short[] get_Foo_array(long jarg0);

}

c++ code:

class Foo {

public:

unsigned char array[10];

};

extern "C"{

JNIEXPORT void JNICALL Java_example_set_1Foo_1array(JNIEnv *jenv, jclass jcls, jlong jarg0, jshortArray jarg1) {

Foo *arg0 ;

unsigned char *arg1 ;

int i ;

jshort* jarg1_carray ;

jsize jarg1_len = jenv->GetArrayLength(jarg1) ;

arg0 = *(Foo **)&jarg0;

jarg1_carray = jenv->GetShortArrayElements(jarg1, 0);

arg1 = (unsigned char *) malloc(jarg1_len * sizeof(unsigned char ));

for(i=0; i<jarg1_len; i++)

arg1 = (unsigned char )jarg1_carray;

{

int i;

for (i=0; i><10; i++)

arg0->array = arg1;

}

jenv->ReleaseShortArrayElements(jarg1, jarg1_carray, 0);

free(arg1);

}}

extern "C"{

JNIEXPORT jshortArray JNICALL Java_example_get_1Foo_1array(JNIEnv *jenv, jclass jcls, jlong jarg0) {

jshortArray jresult = 0 ;

Foo *arg0 ;

unsigned char *result ;

jshort* jnitype_ptr = 0 ;

int k ;

arg0 = *(Foo **)&jarg0;

result = (unsigned char *)(unsigned char *) (arg0->array);

jresult = jenv->NewShortArray(10);

jnitype_ptr = jenv->GetShortArrayElements(jresult, 0);

for (k=0; k<10; k++)

jnitype_ptr[k] = (jshort)result[k];

jenv->ReleaseShortArrayElements(jresult, jnitype_ptr, 0);

return jresult;

}}

The code comes from the output of swig (www.swig.org) - a tool which generated the JNI and Java code given the C++ class definition above.

Guest at 2007-7-2 16:11:58 >