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Editorial Team
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Asked: 2026-05-27T01:14:17+00:00

In an Android app, using NDK, I’m accessing a local file using fopen ,

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In an Android app, using NDK, I’m accessing a local file using fopen, fclose, etc. My app started out as HellloJNI (the supplied example). Accessing the file actually worked initially. The file path I used was "/data/data/com.example.hellojni/files/Test.txt".

Naturally I don’t want my app to be called HelloJNI forever, so I changed the package name (manifest/@package in AndroidManifest.xml) from com.example.hellojni to com.example.mytest. Accordingly, I use a different file path: "/data/data/com.example.mytest/files/Test.txt". But the same call to fopen("[...]", "w+") that used to succeed now fails.

Any ideas?

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1 Answer

  1. Editorial Team

    It works after manually creating the files folder below /data/data/com.example.mytest. In a way, it’s obvious, but I still don’t fully understand it, because I never created explicitly the files folder below /data/data/com.example.hellojni. So where did that one come from?

    Edit:

    Apparently calling getFilesDir creates the Files folder implicitly, so that mystery is solved 🙂

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