working static library gmath with gpower method

app/CMakeLists.txt

@@ -5,6 +5,14 @@
 
 cmake_minimum_required(VERSION 3.4.1)
 
+
+# configure import libs
+set(distribution_DIR ${CMAKE_SOURCE_DIR}/../distribution)
+
+add_library(lib_gmath STATIC IMPORTED)
+set_target_properties(lib_gmath PROPERTIES IMPORTED_LOCATION
+    ${distribution_DIR}/gmath/lib/${ANDROID_ABI}/libgmath.a)
+
 # Creates and names a library, sets it as either STATIC
 # or SHARED, and provides the relative paths to its source code.
 # You can define multiple libraries, and CMake builds them for you.
@@ -32,13 +40,15 @@ find_library( # Sets the name of the path variable.
               # you want CMake to locate.
               log )
 
+target_include_directories(native-lib PRIVATE
+                           ${distribution_DIR}/gmath/include)
+
+
 # Specifies libraries CMake should link to your target library. You
 # can link multiple libraries, such as libraries you define in this
 # build script, prebuilt third-party libraries, or system libraries.
 
 target_link_libraries( # Specifies the target library.
                        native-lib
-
-                       # Links the target library to the log library
-                       # included in the NDK.
+                       lib_gmath
                        ${log-lib} )

app/build.gradle

@@ -11,7 +11,7 @@ android {
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
         externalNativeBuild {
             cmake {
-                cppFlags ""
+                arguments '-DANDROID_STL=c++_static'
             }
         }
     }

app/src/main/cpp/native-lib.cpp

@@ -1,5 +1,6 @@
 #include <jni.h>
 #include <string>
+#include <gmath.h>
 
 extern "C"
 JNIEXPORT jstring
@@ -8,6 +9,7 @@ JNICALL
 Java_farzi_labs_helloworldexternallibs_MainActivity_stringFromJNI(
         JNIEnv *env,
         jobject /* this */) {
-    std::string hello = "Hello from C++";
+    std::string result = std::to_string(gpower(4));
+    std::string hello = "The square of 4 is : "+result;
     return env->NewStringUTF(hello.c_str());
 }

distribution/gmath/include/gmath.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+#ifndef __POWER_HPP__
+#define __POWER_HPP__
+/*
+ * return pow(2, n)
+ */
+#ifdef __cplusplus
+extern "C"
+#endif // __cplusplus
+           unsigned gpower(unsigned n);
+
+#endif //__POWER_HPP__