File access from native code

[sofarsogood]

hi

I need to create/access files residing in my application's folder in
internal memory(data/data/com.myapp.myappname) from native code.
fopen() fails with permission denied error.

I am able to access/create files in the sd card, but it fails when I
write to internal memory. Can anybody suggest a solution?

Thx

[Ryan Routon]

Basically you have to pipe a file descriptor and offset from java to
your c code.

It was discussed in length here:
http://groups.google.com/group/android-ndk/browse_thread/thread/4e25a5dfd46f8fea

[Dianne Hackborn]

First don't use raw paths.  You should use JNI to call Context.getFilesDir() to get the directory at which to put your files.

Given you have the correct path, you can just use normal C APIs to read and write files there; nothing else special is needed.

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[sofarsogood]

So, would passing the correct dir from JNI be enough?

Or, would I need to open the file in JNI and pass fd as suggested by
Ryan?

On Apr 18, 11:23 am, Dianne Hackborn <hack...@android.com> wrote:
> First don't use raw paths.  You should use JNI to call Context.getFilesDir()
> to get the directory at which to put your files.
>
> Given you have the correct path, you can just use normal C APIs to read and
> write files there; nothing else special is needed.
>
>
>
>
>
>
>
>
>
> On Mon, Apr 18, 2011 at 8:48 AM, sofarsogood <anuragbha...@gmail.com> wrote:
> > hi
>
> > I need to create/access files residing in my application's folder in
> > internal memory(data/data/com.myapp.myappname) from native code.
> > fopen() fails with permission denied error.
>
> > I am able to access/create files in the sd card, but it fails when I
> > write to internal memory. Can anybody suggest a solution?
>
> > Thx
>
> > --
> > You received this message because you are subscribed to the Google Groups
> > "android-ndk" group.
> > To post to this group, send email to andro...@googlegroups.com.
> > To unsubscribe from this group, send email to
> > android-ndk...@googlegroups.com.
> > For more options, visit this group at
> >http://groups.google.com/group/android-ndk?hl=en.
>
> --
> Dianne Hackborn
> Android framework engineer

> hack...@android.com

[sofarsogood]

More details -

These files will be created by the native code. So, passing an fd from
the JNI layer would be a difficult implementation for me. There is no
discussion on file creation from native environment in the link
(thread) posted by Ryan.

[Dianne Hackborn]

You just need to have the files directory.  You can freely create files within that directory.

hac...@android.com

[sofarsogood]

Thx. I'll try and let you know.

[sofarsogood]

It worked. Thx.

Is there a way to get this path from within the native code? Its
difficult for me to pass the path down the layers to the native
component that creates the files.

[Dianne Hackborn]

Unfortunately you need to write the JNI code to do so.

hac...@android.com

[sofarsogood]

Okay.

Thx for your help.

On Apr 20, 4:52 pm, Dianne Hackborn <hack...@android.com> wrote:
> Unfortunately you need to write the JNI code to do so.
>

[Chris Stratton]

On Apr 20, 3:54 pm, sofarsogood <anuragbha...@gmail.com> wrote:

> Is there a way to get this path from within the native code? Its
> difficult for me to pass the path down the layers to the native
> component that creates the files.

On startup you could discover the path in java and jni call a simple
function which copies it into a globally accessible native buffer for
use by later native functions.