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POC++ and JNI - How to pass an array into a jfloatArray
 

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  1. POC++ and JNI - How to pass an array into a jfloatArray
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    <p>I have been messing with my own little project to teach myself the android ndk using c++ and jni but I can't figure out how to pass the data from a java float array to the c++ array. I have used the jni set up. Most the tutorials I find are either too simple and don't explain enough or are too complicated and go over my understanding at the moment. So, can some one just point me to a simple example of an array being passed from java to c++, then have some method/function performed on the data and sent back to java. </p> <p>Heres my attempt so far but I have two errors left in the way. Im not sure if the rest of the syntax is up to par either but I don't see anything at compile time.</p> <pre><code>#include &lt;iostream&gt; #include &lt;Eigen/Dense&gt; #include &lt;math.h&gt; #include &lt;jni.h&gt; using namespace Eigen; Vector3f vec; Vector3f vec2; Vector3f vecRtrn; void vecLoad(float x, float y, float z, float x2, float y2, float z2){ vec(0) = x; vec(1) = y; vec(2) = z; vec2(0) = x2; vec2(1) = y2; vec2(2) = z2; } void vecAdd(Vector3f vecA, Vector3f vecB){ vecRtrn = vecA+vecB; } extern "C" { JNIEXPORT jfloatArray JNICALL Java_jnimath_act_JnimathActivity_test (JNIEnv *env, jobject obj, jfloatArray fltarray1, jfloatArray fltarray2){ float array1[3]; jfloatArray flt1 = fltarray1; jfloatArray flt2 = fltarray2; //flt1 = env-&gt;GetFloatArrayElements( fltarray1,0); //flt2 = env-&gt;GetFloatArrayElements( fltarray2,0); vecLoad(flt1[0], flt1[1], flt1[2], flt2[0], flt2[1], flt2[2]); vecAdd(vec, vec2); array1[0] = vecRtrn[0]; array1[1] = vecRtrn[1]; array1[2] = vecRtrn[2]; return array1; }; } </code></pre> <p>And these are the errors at compile time</p> <pre><code> $ /cygdrive/c/android-ndk-r7/ndk-build Compile++ thumb : test &lt;= test.cpp jni/test.cpp: In function '_jfloatArray* Java_jnimath_act_JnimathActivity_test(JNIEnv*, _jobject*, _jfloatArray*, _jfloatArray*)': jni/test.cpp:42: error: cannot convert '_jfloatArray' to 'float' for argument '1' to 'void vecLoad(float, float, float, float, float, float)' jni/test.cpp:49: error: cannot convert 'float*' to '_jfloatArray*' in return make: *** [obj/local/armeabi/objs/test/test.o] Error 1 </code></pre>
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