Load shared library by path at runtime

Question

I am building a Java application that uses a shared library written in C++ and compiled for different operating systems. The problem is, that this shared library itself depends on an additional library it normally finds under the appropriate environment variable (PATH, LIBRARY_PATH or LD_LIBRARY_PATH).

I can - but don't want to - set these environment variables. I'd rather load the needed shared libraries from a given path at runtime - just like a plugin. And no - I don't want any starter application that starts a new process with a new environment. Does anybody know how to achieve this?

I know that this must be possible, as one of the libraries I use is capable of loading its plugins from a given path. Of course I'd prefer platform independent code, but if this ain't possible, seperate solutions for Windows, Linux and MacOS would also do it.

EDIT I should have mentioned that the shared library I'd wish to use is object oriented, which means that a binding of single functions won't do it.

Answer 1

Un UNIX/Linux systems you can use dlopen. The issue then is you have to fetch all symbols you need via dlsym

Simple example:

typedef int (*some_func)(char *param);  void *myso = dlopen("/path/to/my.so", RTLD_NOW); some_func *func = dlsym(myso, "function_name_to_fetch"); func("foo"); dlclose(myso); 

Will load the .so and execute function_name_to_fetch() from in there. See the man page dlopen(1) for more.

Answer 2

On Windows, you can use LoadLibrary, and on Linux, dlopen. The APIs are extremely similar and can load a so/dll directly by providing the full path. That works if it is a run-time dependency (after loading, you "link" by calling GetProcAddress/dlsym.)