Shared library on OS X (rpath issue?)

[jamesa917]

I'm learning about shared libraries in C++ but I'm struggling to run a program when the shared library .so file isn't in the same directory as the executable. As a minimal example, I have the file "print_hw.cpp" in ./shared/:

#include <iostream>

void print_hw() {
  std::cout << "Hello world!" << std::endl;
}

Which I compile with:

g++ -c -fPIC -o print_hw.o print_hw.cpp
g++ -shared -o libprint_hw.so print_hw.o

Then in ./ I have "main.cpp":

void print_hw();

int main() {
  print_hw();

  return 0;
}

I then compile this with:

g++ -L./shared -Wl,-rpath,./shared -o test main.cpp -lprint_hw

This all compiles fine, but when I run "./test" I get:

dyld: Library not loaded: libprint_hw.dylib
Referenced from: ..././test
Reason: image not found

unless I put libprint_hw.so in the same directory as the executable, when it works.

I've been following the guide on Cprogramming.com http://www.cprogramming.com/tutorial/shared-libraries-linux-gcc.html which is intended for C and Linux - am I missing something to make this work on OS X?

Thanks for any help.

[jamesa917]

Well I think I figured this out, and I believe it's an OS X thing. If I compile my shared library with:

g++ -dynamiclib -o libprint_hw.dylib -install_name @loader_path/shared/libprint_hw.dylib print_hw.cpp

and then compile my program with:

g++ -o test -Lshared -lprint_hw main.cpp

it all works. This blog post was useful in working this out:
https://mikeash.com/pyblog/friday-qa-2009-11-06-linking-and-install-names.html

Hopefully this might help someone else in future!