I have an external compiled static C++ library that I'm using in my android application. This library is reading a file. I want to know if there is a way I can "redirect" the function that's reading the file so that it reads another file.
So if it does:
fopen("myfile.txt", "rb");
I want to intercept it and to do this instead:
fopen("myotherfile.txt", "rb");
In Objective-C I use MethodSwizzling. Is there something similar I can do in C++ or the android NDK?
Short of editing the binary (with uncertain results), your best option is to use a symlink... if you're just doing it for development purposes, you could use adb shell into your test device to create the symlink.
http://developer.android.com/guide/developing/tools/adb.html#issuingcommands
How about contact the author of the library and ask them to introduce a parameter? Having hard-coded file paths is a lousy design anyway, the library will be better off.
Related
Basically, I have a C++ program that finds the sum of two numbers given. I need to provide the two numbers to the C++ program as input using my android app and then display the result in my android app. I guess I need to use parcelable class. Can someone please tell me the steps to be followed?
Edit: I forgot to mention that the C++ program that I intend to communicate with is an executable program (sum.exe)
To run a C++ executable on Android, you can use something like Runtime.exec("sum 1 2"). There are a lot of tutorials, e.g. https://www.mkyong.com/java/how-to-execute-shell-command-from-java/. The output (stdout and stderr) can be parsed, too. A more sophisticated way is to use ProcessBuilder, but the idea is the same.
If you want your executable to keep running in background, and send the numbers to crunch once in a while, you can either use input pipe, or some IPC protocol. Shared memory works well, see e.g. How to use Shared Memory (IPC) in Android.
You can use JNI code, take a look here:
https://github.com/mkowsiak/jnicookbook/tree/master/recipes/recipeNo025
where you can find super simple code with C++ being called via JNI wrapper from Java.
I have a video(.mp4) file in my SDCard,I want to reduce a size of .mp4 file and upload this file to a server.
One way you can do this is to use ffmpeg.
There are several ways of using ffmpeg in an Android program:
use the native libraries directly from c using JNI
use a library which provides a wrapper around the 'ffmpeg' cmd line utility (also uses JNI in the wrapper library)
call ffmpeg cmd line via 'exec' from within you Android app
Of the three, I personally have used the wrapper approach in the past and found it worked well. IMHO, the documentation and examples available with the native libraries represented quite a steep learning curve.
Note, if you do use 'exec' there are some things it is worth being aware of - see bottom of this answer: https://stackoverflow.com/a/25002844/334402.
The wrapper does have limitations - at heart, the ffmpeg cmd line tool is not intended to be used this way and you have to keep that in mind, but it does work. There is an example project available on github which seems to have a reasonable user base - I did not use it myself but I did refer to it and found it useful, especially for an issue you will find if you need to call your ffmpeg wrapper more than once from the same activity or task:
https://github.com/jhotovy/android-ffmpeg
See this answer (and the questions and answers it is part if) for some more specifics on the 'calling ffmpeg two times' solution:
https://stackoverflow.com/a/28752190/334402
I have an algorithm and some other code which is in MATLAB and I want to use it in my Android application.
How can I do this?
Can I make a jar file from MATLAB for use with Android?
I have to do something else?
If you have an additional product, MATLAB Builder JA for Java, you can produce a .jar file from your MATLAB code.
However, the .jar file requires the MATLAB Compiler Runtime (a freely redistributable component that you get with MATLAB Compiler and MATLAB Builder products) to be present. The MCR has a much larger footprint than is suitable for the typical Android device (it's like a copy of MATLAB itself, without the user interface).
You could think about either
Running your MATLAB .jar file remotely on a server, and having your Android application connect to it, or
Instead of using MATLAB Compiler and Builder products, use MATLAB Coder, which will convert a subset of the MATLAB language directly into C code. This C code doesn't require the MCR, and could be compiled to run directly on Android. Make sure your MATLAB algorithm falls within, or can be expressed in, the appropriate subset of the MATLAB language.
Edit: As of R2015a, functionality from MATLAB Builder JA for Java has been replaced by a new product, MATLAB Compiler SDK.
I am the developer of Addi. http://addi.googlecode.com Addi is quickly becoming a full port of Octave (which is an open source tool that uses Matlab syntax). Addi is going to have intents for other applications to use it as their math engines or plotting engines. So, if you can run your code on Octave, then very soon you will be able to run it on Android.
Our only option is to get C++ code from M code using MATLAB Coder toolbox, that generates standalone C and C++ code from MATLAB® code. It supports only some subset of all Matlab functions, therefore might be not suitable for your needs.
Having C code you can compile it using NDK. MATLAB Compiler is not an option here.
A new feature in Matlab 2014a:
http://www.mathworks.com/help/simulink/samsung-galaxy-android-devices.html
You can now directly install (limited set of) models to Samsung Android devices, and this should work actually on any Android device.
You can convert matlab code into python and then use the python code in the android .There are many tools to do this conversion. Python goes well with android than matlab.
You have 2 options,
Create a JAR and include in your Java Application and start using it. (I have not tested this by creating a JAR outside Eclipse)
You can code the same thing in C and use Android NDK to process it. (This will be faster and safer way)
Background:
I have working C++ code on linux that uses Boost IPC to access shared memory, and I want to port it to android. I downloaded and built the Boost-for-Android project found here: https://github.com/MysticTreeGames/Boost-for-Android.
Problem:
However when I try to create a boost named mutex like this:
boost::interprocess::named_mutex named_mtx(boost::interprocess::open_or_create, "my_mutex");
I get an exception saying "no such file or directory" with a native code 2.
Additional information:
When I searched for how to use shared memory on android, it looks ashmem and Binder are popular methods, and I can't find references to them at all in the ported Boost IPC code.
Questions:
What is the reason for the "no such file or directory" error?
Can someone confirm that the Boost-for-Android IPC part works?
By default Boost does not look for a common place where to share data on Android. It was not built this way. To make it work modify the file
/boost/interprocess/detail/os_file_functions.hpp
Find the following line an add /sdcard
const char *names[]={ "/sdcard", ......
After doing that use the library and give to your application Read/Write external storage permission.
You are good to go.
PD: Please be carefull. I have problems using Mutex and conditional variables in Android because the process was taking 100% the CPU.
I followed the way provided by #user3645767 but it didn't work. But I solved it by revision the file 'interprocess/detail/shared_dir_helpers.hpp'
line 109
to change the dir_path in get_shared_dir_root()
#elif defined __ANDROID__
dir_path="/data"
#else
dir_path="/tmp"
I would like to use the facedetection in opencv cpp to use it in an android app. I have compiled jni successfully. But I wonder how would i use the haarcascades. I can store in sdcard and read it from there. Is there any other way i can use the xml files directly from the project?
There is a c++ example called facedetect coming with the opencv superpack. I'm running OpenCV-2.3.1 myself and it's located in this folder: ../opencv-2.3.1/samples/c/
The sample uses haarcascades and this might be your best bet for facedetection. If you can use the Android NDK with proper JNI calls from a .cpp file then you shouldn't have any problems to use this sample.
I'm working on a similar thing myself but haven't tried it myself yet. Should be implementing the thing somewhere next week but can't guarantee it. Let me know if this works out for you