With Boost:
Breakpoint 1, main () at test.cpp:18
16	      dll::shared_library lib ("utils.so");
(gdb) n
(gdb) p add
$1 = (int (*)(int, int)) 0x0
(gdb) n
18	      add = lib.get <typeof(add)> ("add");
(gdb) p add
$2 = (int (*)(int, int)) 0x6c8948e8245c8948
(gdb)

With dlopen:

(gdb) p add
$2 = (int (*)( int, int)) 0x7ffff5fe4c20
(gdb)