Android NDK Write File

http://stackoverflow.com/questions/4731314/android-ndk-write-file

1. You can always access the directory in which your app is placed.

   This directory is usually :

   data/data/<Your_package_name_usuallycom.android.appName>/files/<your_filename>

   but better use getFilesDir() to ensure valid filepath with future version changes of android.

2. If you wanna use external storage instead, make sure you place this line of code in your app manifest to gain permission.

   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
   

   Then use the sdcard directory :

   getExternalStorageDirectory(); //usually : /sdcard/<your_filename>

3. Otherwise, you can root the device and gain access to the whole filesystem. But you'll have to request all of your app users to get root access on their device before using your application. Some games use this way of doing things, but I wouldn't recommend it. If you still wanna do this, lookup Superuser app for android, it's free and trustable.

Once you have the android directory, just create a JNI native method that receive a jstring parameter, and you set it up inside your native code. Convert it into a std::string, and you'll be ready to use it with fopen().

//Inside your java activity
File f = this.getApplicationContext().getFilesDir(); 
LibLoader.setupArchiveDir(f.toString());

//Inside your JNI wrapper
JNIEXPORT bool JNICALL Java_com_android_appName_LibLoader_setupArchiveDir(JNIEnv * env, jobject obj, jstring dir)
{
        const char* temp = env->GetStringUTFChars(dir, NULL);
    std::string stringDir(temp);

        // Will be receive as a std::string inside C++ code 
    MyNativeObjectInC++->SetupArchiveDir(stringDir);
}