I want to call C++ code from java using JNI. I already followed many tutorials on this, and all are working, when the C++ code is "simple". But the C++ code which I am going to call inludes the opencv library and uses various functions of it. And this is, where I get problems... What I am doing is the following:
1.) g++ -fPIC -shared -I/usr/lib/jvm/java-1.7.0-openjdk-i386/include -I/usr/lib/jvm/java-1.7.0-openjdk-i386/include/linux -o libHello.so Hello.cpp
which creates the .so file.
2.) I copy my created .so file to the directory where I use it, just as I did with the tutorials, and load it:
static {
System.loadLibrary("Hello");
}
But I get an UnSatisfiedLinkError with undefined symbol: _ZTTN2cv4SURFE
Most probably there is an error in the first step, such that it can not find my opencv library. But I don't know what the correct command would be.
ldd -d libHello.so produces:
linux-gate.so.1 => (0xb777d000)
libstdc++.so.6 => /usr/lib/i386-linux-gnu/libstdc++.so.6 (0xb765e000)
libgcc_s.so.1 => /lib/i386-linux-gnu/libgcc_s.so.1 (0xb7640000)
libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0xb7496000)
libm.so.6 => /lib/i386-linux-gnu/libm.so.6 (0xb746a000)
/lib/ld-linux.so.2 (0xb777e000)
undefined symbol: _ZTTN2cv4SURFE (./libHello.so)
undefined symbol: _ZTV11CvStatModel (./libHello.so)
undefined symbol: _ZTVN2cv24BackgroundSubtractorMOG2E (./libHello.so)
undefined symbol: _ZTVN2cv4SURFE (./libHello.so)
undefined symbol: _ZTV5CvSVM (./libHello.so)
edit:
For anyone else getting the same problem:
1.) As some people mentioned, I was not linking against the opencv library.
2.) But this was not enough. I was using this command, as it is also done in some tutorials:
g++ -shared -I/usr/lib/jvm/java-1.7.0-openjdk-i386/include -I/usr/lib/jvm/java-1.7.0-openjdk-i386/include/linux -I/usr/local/include/opencv -L/usr/local/lib -lopencv_nonfree -lopencv_features2d -lopencv_core -lopencv_highgui Hello.cpp -o libHello.so
which caused the undefined symbol error when doing "ldd"
I changed the command to:
g++ Hello.cpp -shared -I/usr/lib/jvm/java-1.7.0-openjdk-i386/include -I/usr/lib/jvm/java-1.7.0-openjdk-i386/include/linux -I/usr/local/include/opencv -L/usr/local/lib -lopencv_nonfree -lopencv_features2d -lopencv_core -lopencv_highgui -o libHello.so
i.e. I just wrote Hello.cpp directly after g++ instead at the end. And this solved the problem.
I don't know why this is working and the previos one didn't. But maybe someone can tell me.
c++filttells me that first symbol isVTT for cv::SURF. – Joe Z