Issues Accessing /sdcard/ using fopen.

[Gregory Ray]

Hi Guys,

I am receiving a NULL file when using:

FILE* file = fopen((data_path + "/" + path).c_str(),"w+");

Where as data_path = android.os.Environment.getExternalStorageDirectory().getAbsolutePath() passed in from JNI.

Where as path is arbitrary but the concatenated string = "/sdcard/test.mp3" (this is from my logs).

test.mp3 does not exist but my expectation is that it will be created with the w+ setting.

I created my AVD with an sdcard using:

./android create avd -n withsdcard -t 6 -c 25M

And also my android manifest has the following permission:

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

(I verified this by looking at the application settings)

Another thing is that tmpfile() returns NULL as well, although I can see reasons why tmpfile may not work I would expect the fopen("/sdcard/foo.bar","w+") to work. Did I miss something?

I am also ok writing to anywhere in the filesystem but it is my understanding that this is the only place we can write files from the NDK, is this correct?

I feel that I have exhausted all known possibilities at the moment, please help.

--
Gregory Ray
COO, Seek Mobile Interactive, Inc.

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[Sean Hodges]

I can't see anything wrong with your approach, though it's difficult
to tell without seeing how you wired up your JNI calls. Have you
checked whether there is a null character at the end of data_path?

Also thought I'd point you at the StackOverflow solution, in case you
haven't seen it:
http://stackoverflow.com/questions/1992953/file-operations-in-android-ndk

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[fadden]

On Mar 8, 3:31 am, Gregory Ray <gr...@seekmobileinteractive.com>
wrote:

> I am receiving a NULL file when using:
> FILE* file = fopen((data_path + "/" + path).c_str(),"w+");

Two thoughts:

(1) try plain fopen("/sdcard/test.mp3", "w+") to rule out any
weirdness with the string stuff
(2) print the return value from errno (LOGW("fopen(%s) failed: %s",
filename, strerror(errno));)

Hopefully these will provide a clue.

In the spirit of "is it plugged in", do an "echo blah > /sdcard/test ;
cat /sdcard/test" from the adb shell before running your test just to
make sure the SD card is mounted writable.

[Gregory Ray]

This is what I am seeing from the log:

failed: No such file or directory

Any ideas what might cause this?

Thanks,

Greg

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[Dianne Hackborn]

Are you sure the SD card is mounted?  Have you tried creating that file with the shell?  Have you tried creating the file with the Java APIs?  There is absolutely no difference in functionality for accessing files via either java or the NDK (the java APIs are just wrappers for calling the native file functions), and apps can definitely write to the SD card if they have the permission, so it most likely it something generally wrong unrelated to the NDK.

Dianne Hackborn
Android framework engineer
hac...@android.com

Note: please don't send private questions to me, as I don't have time to provide private support, and so won't reply to such e-mails.  All such questions should be posted on public forums, where I and others can see and answer them.

[Gregory Ray]

Dianne,

The shell revealed the problem to me once I saw the file was actually being created. Thanks for working late and the help.

-Greg