Android Studio JNI编程以及NDK环境配置

#include <jni.h>
#include <android/log.h>
#include <assert.h>
#include <stdio.h>
/* 输出Log的宏 */
#ifndef LOG
#define LOG_TAG "imgprocess"
#define ALOGD(...)             __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__);
#define ALOGE(...)             __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__);
#define ALOGV(...)             __android_log_print(ANDROID_LOG_VERBOSE, LOG_TAG, __VA_ARGS__);
#endif LOG
#ifndef NELEM
# define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0])))
#endif
jstring native_hello(JNIEnv* env, jobject thiz)
{
    return env ->NewStringUTF("hello world from jni~");
}
//native函数所在java类的位置
static const char *classPathName = "com/test/hc/MainActivity";
// 映射表，这里将我们java函数和c函数对应起来
static JNINativeMethod gMethods[] = {
        {"native_hello", "()Ljava/lang/String;", (void*)native_hello},
};
int registerNativeMethods(JNIEnv* env, const char* className,
                                    JNINativeMethod* gMethods, int numMethods)
{
    jclass clazz;
    clazz = env->FindClass(className);
    if (clazz == NULL) {
        ALOGE("Native registration unable to find class '%s'", className);
        return JNI_FALSE;
    }
    if (env->RegisterNatives(clazz, gMethods, numMethods) < 0) {
        ALOGE("RegisterNatives failed for '%s'", className);
        return JNI_FALSE;
    }
    return JNI_TRUE;
}
//static
int register_my_jni_methods(JNIEnv* env)
{
    return registerNativeMethods(env, classPathName, gMethods, NELEM(gMethods));
}
// 在我们load该so库的时候，JNI_OnLoad将会自动被调用，来注册JNI函数
jint JNI_OnLoad(JavaVM* vm, void*)
{
    JNIEnv* env = NULL;
    jint result = -1;
    if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
        ALOGE("ERROR: GetEnv failed\n");
        goto bail;
    }
    assert(env != NULL);
    if (register_my_jni_methods(env) < 0) {
        ALOGE("ERROR: native registration failed\n");
        goto bail;
    }
    ALOGE("SUCCESS: native registration successed\n");
    result = JNI_VERSION_1_4;
    bail:
    return result;
}