Simple example of strong and weak pointers on Android using RefBase class

Here is a simple example explaining the usage of strong and weak pointers using android's RefBase class and the Android.mk to compile the same. Its a modified version of code written by Daniel in the following link.

http://himmele.blogspot.com/2012/03/androids-c-reference-counting.html

strong_pointer.cpp file: 

#include <stdio.h>

#include "utils/RefBase.h"

namespace android { 

class RefTest : public RefBase {

public:

    RefTest(int32_t id) : mID(id) {

        printf("RefTest ctor: %d\n", mID);

    }

    virtual ~RefTest() {

        printf("RefTest dtor: %d\n", mID);

    }

    int32_t id() const {

        return mID;

    }

private:

    int32_t mID;

};

int strong_pointer() {

    sp<RefTest> ref1 = new RefTest(1);

    sp<RefTest> ref5;

    {

    sp<RefTest> ref2 = new RefTest(2);

    ref5 = ref2; // comment this out and check when the destructor of ref2 is called

    }

    wp<RefTest> ref3 = ref1;

    sp<RefTest> ref4 = ref3.promote();

    if (ref4 == NULL) {

        printf("RefTest object is destroyed\n");

    } else {

        printf("RefTest object %d is still around\n",

            ref4->id());

    }

    ref4 = NULL;

    ref1 = NULL; // comment this out to check to check change in prints

    ref4 = ref3.promote();

    if (ref4 == NULL) {

        printf("RefTest object is destroyed\n");

    } else {

        printf("RefTest object %d is still around\n",

            ref4->id());

    }

    printf("Before return \n"); 

    return 0;

}

}

int main()

{

    android::strong_pointer();

    return 0;

}

Android.mk file:

LOCAL_PATH:= $(call my-dir)

include $(CLEAR_VARS)

LOCAL_SRC_FILES:=                       \

        strong_pointer.cpp            

LOCAL_MODULE:= strong_pointer

LOCAL_SHARED_LIBRARIES := \

        libutils    \

LOCAL_MODULE_TAGS := optional

LOCAL_C_INCLUDES := \

        frameworks/native/include \

include $(BUILD_EXECUTABLE)