C++ can't compile when I use iostream (Linux, CodeBlocks) - c++

Question

I want to use C++ Code in Java. I know I have to use JNI. And now I want to compile a shared library in C++ on Linux. I using the Code::Blocks 16.01 IDE and the GNU GCC Compiler.
And now I want to compile this very simple code:
#include <iostream>
void sayHello ()
{
std::cout << "Hello from C++" << std::endl;
}
(I know that I also have to include some more to use this library later in java, but this was just my first test, if it compiles)
The Build log is:
g++ -shared obj/Debug/main.o -o bin/Debug/libnativetest.so
/usr/bin/ld: obj/Debug/main.o: Die Umlagerung von
obj/Debug/main.o: error adding symbols: Ungültiger Wert
collect2: error: ld returned 1 exit status
Process terminated with status 1 (0 minute(s), 0 second(s))
1 error(s), 0 warning(s) (0 minute(s), 0 second(s))
The Build messages:
||error: ld returned 1 exit status|
||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|
When I just compile the method without#include <iostream> (and sure without cout) it works.
I have tested with another header file like #include <string> and this works.
When I create a project not as a shared library instead a Console Application I can use <iostream>.
I am new to C++ and Code::Blocks therefore if you need some more info please help me where I can find this information.

Answer 1

I do not use Code blocks, so I have no idea how it decided to leave out the fPIC flag. If you try to build it on the command line with
g++ main.cpp -o main.o
The gcc (v5.4 in my case) prompts you to add -fPIC flag, with with the error disappears and the compilation succeeds. fPIC stands for position independent code. i.e., the function addresses (jump addresses) are not hard coded but are left blank. The loader, when it needs the .so, loads it to the memory and then fills the jump addresses dynamically. (-fpic could also work, it is for short jumps, whereas fPIC accommodates also long jumps, i.e., bigger jump ranges at the cost of binary size.)