JNI Pass Char* 2D array to JAVA Code

Question

I want to pass the following pointer array through the JNI layer from C code

char *result[MAXTEST][MAXRESPONSE] = {
    { "12", "12", "" },
    { "8",  "3",  "" },
    { "29", "70", "" },
    { "5",  "2",  "" },      
    { "42", "42", "" }
};

In java code I have written the following declaration

public static native String[][] getResult();

I am confused how to pass that array through JNI layer to Java code??? Following is the JNI layer description

JNIEXPORT jobjectArray JNICALL Java_com_example_CheckResult_getResult
  (JNIEnv *env, jclass thiz) {
Confused over here ????
}

This is a duplicate of stackoverflow.com/questions/6070679/… — jop
– jop, Commented Apr 12, 2013 at 14:01
While you can do so (you essentially have to create multiple Java objects, including arrays, arrays as array elements, and strings), I'd recommend that you re-think your interface to instead return a single block of data (maybe a single byte buffer with NUL terminators between strings) and let the Java side re-interpret it if necessary. The general complexity of turning a multi-dimensional C array in JNI into a multi-dimensional Java array is a lot higher than constructing the multi-dimensional array on the Java side (assuming that your really need that format) from simpler data. — technomage
– technomage, Commented Apr 12, 2013 at 16:17

Community · Accepted Answer · 2017-05-23 12:06:25Z

2

Finally after hours working on jop's shared link, I could solve my problem. The code goes as below:

JNIEXPORT jobjectArray JNICALL Java_com_example_CheckResult_getResult(JNIEnv *env, jclass thiz) {
    jboolean flag = JNI_TRUE;
    jclass stringClass = (*env)->FindClass(env, "java/lang/String");
    jobjectArray row;
    jobjectArray rows;

    jsize i, j;
    for(i=0; i<5; i++) {
        row = (*env)->NewObjectArray(env, MAXRESPONSE, stringClass, 0);
        for(j=0; j<3; j++) {
            (*env)->SetObjectArrayElement(env, row, j, (*env)->NewStringUTF(env, userResponse[i][j]));
        }

        if(flag == JNI_TRUE) {
            flag = JNI_FALSE;
            rows = (*env)->NewObjectArray(env, MAXTEST, (*env)->GetObjectClass(env, row), 0);
        }

        (*env)->SetObjectArrayElement(env, rows, i, row);
    }

    return rows;
}

edited May 23, 2017 at 12:06

CommunityBot

11 silver badge

answered Apr 15, 2013 at 13:04

AndroidDev

2,6476 gold badges31 silver badges41 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

JNI Pass Char* 2D array to JAVA Code

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related