Android Studio NDK return jint

Issue

I have successfully followed this tutorial https://www.youtube.com/watch?v=kFtxo7rr2HQ to learn about building NDK apps with Android Studio.

That tutorial uses a public native String HelloJNI();

That string is set in the HelloJNI.c file

#include "com_example_myapplication_MainActivity.h"
/* Header for class com_example_myapplication_MainActivity */

/*
 * Class:     com_example_myapplication_MainActivity
 * Method:    HelloJNI
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_example_myapplication_MainActivity_HelloJNI
  (JNIEnv *env, jobject obj)
  {
(*env)->NewStringUTF(env, "Hello from jni");
}

and loaded at runtime with

static{
    System.loadLibrary("HelloJNI");
    }

Now Im attempting to do the same thing but retrieve and int not a string public native int getintONE();

I follow the same steps in the tutorial, everything works fine, now my getintONE.c reads

#include "com_example_myapplication_MainActivity.h"
/*
 * Class:     com_example_myapplication_MainActivity
 * Method:    getintONE
 * Signature: ()I
 */
JNIEXPORT jint JNICALL com_example_myapplication_MainActivity_getintONE
   (JNIEnv *env, jobject obj)

What is the equivelant of

JNIEXPORT jstring JNICALL Java_com_example_myapplication_MainActivity_HelloJNI
  (JNIEnv *env, jobject obj)
  {
(*env)->NewStringUTF(env, "Hello from jni");
}

To return an int, not a string.

I've read through many questions here, read tutorial and documentation, most of the stuff I've seen on my research and tried were samples for returning, jint arrays, converting jint to string, and what seem to me to be more involved advanced topics.

Thanks in advance

Solution

A jint is a primitive type, so if you have included jni.h you can simply return one from the function - there is no need to allocate an Object as you were doing with NewStringUTF() for a String.

JNIEXPORT jint JNICALL com_example_myapplication_MainActivity_getintONE(JNIEnv *env, jobject obj) {
      return 1;  //or anything that can be cast to a jint
}

Answered By - Chris Stratton