LDNS : Undefined reference to variables ( C++ )

I'm new to LDNS. I installed ldns by the method they showed in the README file. I tried using their sample code but whenever I compile it using g++ file.cpp I get the following error.

Using virtual box with Ubuntu on MACOS.

/tmp/ccxvsMSZ.o: In function `main':
dns.cpp:(.text+0x1e): undefined reference to `ldns_dname_new_frm_str'
dns.cpp:(.text+0x33): undefined reference to `ldns_resolver_new_frm_file'
dns.cpp:(.text+0x56): undefined reference to `ldns_resolver_query'
dns.cpp:(.text+0x70): undefined reference to `ldns_pkt_rr_list_by_type'
dns.cpp:(.text+0x80): undefined reference to `ldns_rr_list_sort'
dns.cpp:(.text+0x96): undefined reference to `ldns_rr_list_print'
dns.cpp:(.text+0xa2): undefined reference to `ldns_rr_list_deep_free'
dns.cpp:(.text+0xae): undefined reference to `ldns_pkt_free'
dns.cpp:(.text+0xba): undefined reference to `ldns_resolver_deep_free'
collect2: error: ld returned 1 exit status

Any idea what I might be doing wrong?

P.S.: Tried running code on MAC but got the following error.

Undefined symbols for architecture x86_64:
  "_ldns_dname_new_frm_str", referenced from:
      _main in dns-9f53eb.o
  "_ldns_pkt_free", referenced from:
      _main in dns-9f53eb.o
  "_ldns_pkt_rr_list_by_type", referenced from:
      _main in dns-9f53eb.o
  "_ldns_resolver_deep_free", referenced from:
      _main in dns-9f53eb.o
  "_ldns_resolver_new_frm_file", referenced from:
      _main in dns-9f53eb.o
  "_ldns_resolver_query", referenced from:
      _main in dns-9f53eb.o
  "_ldns_rr_list_deep_free", referenced from:
      _main in dns-9f53eb.o
  "_ldns_rr_list_print", referenced from:
      _main in dns-9f53eb.o
  "_ldns_rr_list_sort", referenced from:
      _main in dns-9f53eb.o
ld: symbol(s) not found for architecture x86_64