C++ linux: dlopen can't find .so library

Question

Reworded Question (although it\'s been solved already):

I\'ve been having trouble using dlopen(3) to load a shared object library on linux. The library is part of a

Answer 1

Read the dlopen(3) man page (e.g. by typing man dlopen in a terminal on your machine):

If filename contains a slash ("/"), then it is interpreted as a (relative or absolute) pathname. Otherwise, the dynamic linker searches for the library as follows (see ld.so(8) for further details):

   o   (ELF only) If the executable file for the calling program
       contains a DT_RPATH tag, and does not contain a DT_RUNPATH tag,
       then the directories listed in the DT_RPATH tag are searched.

   o   If, at the time that the program was started, the environment
       variable LD_LIBRARY_PATH was defined to contain a colon-separated
       list of directories, then these are searched.  (As a security
       measure this variable is ignored for set-user-ID and set-group-ID
       programs.)

   o   (ELF only) If the executable file for the calling program
       contains a DT_RUNPATH tag, then the directories listed in that
       tag are searched.

   o   The cache file /etc/ld.so.cache (maintained by ldconfig(8)) is
       checked to see whether it contains an entry for filename.

   o   The directories /lib and /usr/lib are searched (in that order).

So you need to call dlopen("./libLibraryName.so", RTLD_NOW) -not just dlopen("libLibraryName.so", RTLD_NOW) which wants your plugin to be in your $LD_LIBRARY_PATH on in /usr/lib/ etc .... - or add . to your LD_LIBRARY_PATH (which I don't recommend for security reasons).

As Jhonnash answered you should use and display the result of dlerror when dlopen (or dlsym) fails:

  void* dlh = dlopen("./libLibraryName.so", RTLD_NOW);
  if (!dlh) 
    { fprintf(stderr, "dlopen failed: %s\n", dlerror()); 
      exit(EXIT_FAILURE); };

You might want to read some books like Advanced Linux Programming to get some knowledge about Linux system programming in general.

Answer 2

About the dlopen is defined; Dynamic library dlopen error can be checked. Undefined symbol error by this link.