I currently compiled a set of source code in C in Linux and the output is a *.o file which is a object file. This supposedly does image compression. Now I want to use/test this in Android.
Is this possible? I have only tried NDK examples from the Android NDK developer side. Have not came across any reference on how this can be done.
Thanks In Advance,
Perumal
You don't run object code files (*.o). You would need to turn it into an executable. To do this, assuming you are using GCC you would run gcc file1.o file2.o -o executable which would convert a two file program with file1.o and file2.o into an executable called executable.
Object files (ending in .o) usually contain code that is incomplete. For example, if your program uses some library to print something on screen, to produce an executable, you must link your compiled code (the .o file) with the library, so that when the operating system loads the executable knows all the code that will be used. You do this linking with a linker (such as ld in Linux, or /system/bin/linker in Android). In your case, it's easier to let gcc call the linker for you, as Jalfor notes.
The answer is Yes. But you have to do some fair amount of work to see it running on Android.
1) If you are compiling on Linux, it means the object file or the final executable is being built for the x86 or AMD processor(Mostly). But mostly all the mobile devices have ARM processors running on their phones. So, though you have an executable you will not be able to execute it in ANdroid if it is not built for ARM Cpu. This is what android NDK does exactly.
2) So, we have to build the same code again for Android(ARM), for which we need a cross-compiler and the source code of the object files you are talking about.
3) If you have source code avilable, you can do 2 things again.
To include it in JNI folder, build the shared library and then do the
stuff of calling and all.
Build the code into an executable(Note you need to have main
inside the code) using the android NDK and then push the executable inside Android using
adb.
Now finally you can login and then check the result. In case anything is not clear, please do let me know. I wont mind explaining. Thanks..
Related
In Windows, the dynamic loader always looks for modules in the path of the loaded executable first, making it possible to have private libraries without affecting system libraries.
The dynamic loader on Linux only looks for libraries in a fixed path, in the sense that it is independent on the chosen binary. I needed GCC 5 for its overflow checked arithmetic functions, but since the C++ ABI changed between 4.9 and 5, some applications became unstable and recompiling them solved the issue. While waiting for my distro [kubuntu] to upgrade the default compiler, is it possible to have newly compiled application linking to the new runtime, while packaged application still links to the old library, either by static linkage, or something that mimics the Windows behavior?
One way of emulating it would be to create a wrapper script
#!/bin/bash
LD_LIBRARY_PATH=$(dirname $(which your_file)) your_file
And after the linking step copy the affected library but it is sort of a hack.
You can use rpath.
Let's say your "new ABI" shared libraries are in /usr/local/newapi-libs.
gcc -L/usr/local/newapi-libs
-Wl,-rpath,/usr/local/newapi-libs
program.cpp -o program -lsomething`
The -rpath option of the linker is the runtime counterpart to -L. When a program compiled this way is run, the linker will first look in /usr/local/newapi-libs before searching the system library paths.
More information here and here.
You can emulate the Windows behavior of looking in the executable's directory by specifying -Wl,-rpath,.
[edit] added missing -L parameter and dashes before rpath.
Hi team,
I have three files which I need to compile for testing, btw im using CentOS linux.
source_code.c
library.h
library.c
how do I put the library.h in the gcc library, so I can use it?
how do I compile the source_code.c to use that library?
Thank you very much.
This is basic knowledge of your tools, but you can do this:
#include "library.h" in the include section of the library.c code (at top of the file).
gcc source_code.c library.c in the linux terminal will link and compile both source_code.c and library.c. This will generate an executable named "a.out" (if there were no compilation problems). You can change its name, by adding the option -o name to the gcc command (gcc source_code.c library.c -o mycode will generate an executable named "mycode").
If you really need a library that will be used by a lot of other programs, you can look for "shared libraries", but I think that you are asking for a basic thing.
You dont need this library.h while building and executable (with gcc) as you should have specified the exact location of the library in the source file. All you need to do is gcc sourcefile1.c sourcefile2.c -o exename
I am trying to build c file included by ndk under cygwin
In Android.mk, I add -I/usr/include to LOCAL_FLAGS like
LOCAL_FLAGS := -I/usr/include
And I have checked that openssl does under /usr/include
But when I run ndk-build under by project dir, it output
"fatal error: openssl/ssl.h: No such file or directory"
I think I have specified the include directory, but not solve this problem.
Is there any other way can I try?
You seem to have some gaps in your knowledge:
C code compiles to processor's native instruction set. Your desktop/build machine probably has a different architecture from your Android device(thus a different instruction set).
NDK doesn't just compile, it cross-compiles. It means that the NDK runs on the build machine, but the executable it produces cannot run on the build machine(different instruction sets).
All libraries on your desktop are in your desktop's processoer's instruction set. Thus, you cannot link any program build by the NDK using the desktop's libraries. This means:
No includes from '/usr/include/'
No libs from /lib, /usr/lib, /lib64 or /usr/lib64
No Cygwin packages under on Windows
What you need to do is build your own openssl using the NDK and use that to link against when you build your executable.
Please note that the answer is missing a lot of information (at least 3 Bachelor's level Computer Science courses worth of information).
I got a little confused when it comes to QT and cross compiling
appliations for my arm-linux:
So far I have a linux running on my AT91SAM9263-EK and an appropriate
filessystem including QT libs build via buildroot.
Also I have build QT-4.8 on my ubuntu.
Now I want to build an example application:
I created a makefile in an examples folder in QT on my ubuntu using
qmake; I used the given qmake.conf in mkspecs/qws/linux-arm-g++.
when executing make I get an error because it includes qatomic_i386.h
and the message "error: impossible constraint in 'asm'".
this header file does obviously not match to my arm toolchain.
my question:
how to configure Qt on my ubuntu to build Qt binaries for my embedded linux
on arm? Do I need to include any libs build by the arm toolchain?
any help is appreciated!
regards
EDIT:
I use the -spec flag and pass the path to "mkspecs/qws/arm-linux-g++" where a "qmake.conf" is located. I did not change anything in here because I dont know wich qmake variable are relevant to link to my arm related libs.
So the right compiler is used, which I could verify when the make process starts. But I observed that in a config file called qconfig.h there is an ARCH flag which is set to i386 but I didnt figure out how one can configure this. I dont think I should manually edit this file.
EDIT2:
someone knows whats behind the file qconfig.h?? should I adjust it manually?
I will solve it by myself :)
After struggling a while and scanning the web I got a little deeper involved how everything works together. I did not understand how to generate an executable for my ARM target device. I figured out two things:
do not add your QT path for X11 at the beginning in your PATH variable. this might mess up your cross compilation.
edit the qmake.conf correspondingly. add your libs build for the target device which in my case are located within buildroot. Add theses lines to your qmake.conf file:
QMAKE_CFLAGS += -O3 -march=armv5te
QMAKE_CXXFLAGS += -O3 -march=armv5te
QMAKE_INCDIR_QT = /home/user/arm/toolchain/buildroot-2010.11/output/staging/usr/include
QMAKE_LIBDIR_QT = /home/user/arm/toolchain/buildroot-2010.11/output/staging/usr/lib
I got it running now. thanks to everyone!
Yes, either you provide the Qt libraries in your toolchain or you tell qmake where to find them. Also, I suspect you're calling qmake without the -spec parameters. If you are using the qmake you find in your distribution, it will use the default spec, which is not arm I guess. Add the -spec parameter and point it to the arm mkspec. Also, make sure the generated g++ commands link to the correct Qt libs compiled for arm.
You shall install QtSDK for embedded linux befor you use it to build your application. I'm afraid you just have QtSDK for x86 right now. After QtSDK for embedded linux installed, it has qws/linux-arm-g++ as the default mkspace typically. If you don't have QtSDK for embedded linux, you can build it from source. Then run qmake to create Makefile for you application.
$QTDIR_FOR_ARM/qmake
Reference:
Installing Qt for Embedded Linux and Cross-Compiling Qt for Embedded Linux Applications
I'm trying to implement an open source library that is built using the GNU compiler. (namely, this: https://github.com/mjwybrow/adaptagrams )
I've tried opening and building that source code using VSC++ 6, but it results in over a thousand errors due to the strict nature of the VS compiler I guess. And rather then go through every error and try fix it myself, I was wondering if it's possible to just include the .lib if it is built with the GNU compiler?
EDIT:
Included in the source code linked above is an autogen.sh file.
mkdir -p m4
autoreconf --install --verbose
automake -a --add-missing
./configure
make
Running that with Cygwin results in a few .a library files to be created, which are unusable in VS. Is it ok to just rename these to .lib files?
I've found some stuff online about how to use GCC and create a DLL, but my problem is that I don't know enough about the GNU compiler or makefiles, or the source code in general to be able to change it right now.
Does anybody have any clues on what exactly I'd need to change to get it right? Or even better, has anyone created a DLL using this source code already that would be able to pass it on to me, or let me know what I have to do?
Or could anyone point me towards a similar library that would be compatible with visual studio?
No; you can however build the .dll file with gcc and use the .dll from msvc (with either a hand-crafted include file or a properly formatted one from the beginning, with platform specific import/export macros on top).