My (simple) code links in g++, doesn't link in clang

Question

This is a very simple drill in Stroustrup's PPP, you create 3 files:

my.h:

void print_foo();
void print(int);

my.cpp:

#include <iostream>
#include <string>
#include "my.h"

using namespace std;

void print(int i)
{
    cout << i << '\n';
}

void print_foo()
{
    cout << "Foo" << '\n';
}

and use.cpp:

#include "my.h"

int main()
{
    print_foo();
    print(7);
}

My clang version is Apple LLVM version 7.0.2 (clang-700.1.81) Target: x86_64-apple-darwin15.2.0

This compiles in both clang and g++, but doesn't link in clang. I get this:

$ clang my.cpp use.cpp -std=c++14 -o drill8_1
Undefined symbols for architecture x86_64: 

Does anyone know why this would be the case? I typed the same command into g++, and I got the correct output.

Thank you :)

Here is the rest of the clang output:

    Undefined symbols for architecture x86_64:
  "std::__1::locale::use_facet(std::__1::locale::id&) const", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
  "std::__1::ios_base::getloc() const", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__init(unsigned long, char)", referenced from:
      std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> > std::__1::__pad_and_output<char, std::__1::char_traits<char> >(std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> >, char const*, char const*, char const*, std::__1::ios_base&, char) in my-82a25e.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::~basic_string()", referenced from:
      std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> > std::__1::__pad_and_output<char, std::__1::char_traits<char> >(std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> >, char const*, char const*, char const*, std::__1::ios_base&, char) in my-82a25e.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char> >::sentry::sentry(std::__1::basic_ostream<char, std::__1::char_traits<char> >&)", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char> >::sentry::~sentry()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char> >::operator<<(int)", referenced from:
      print(int) in my-82a25e.o
  "std::__1::cout", referenced from:
      print(int) in my-82a25e.o
      print_foo() in my-82a25e.o
  "std::__1::ctype<char>::id", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
  "std::__1::locale::~locale()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
  "std::__1::ios_base::__set_badbit_and_consider_rethrow()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
  "std::__1::ios_base::clear(unsigned int)", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
  "std::terminate()", referenced from:
      ___clang_call_terminate in my-82a25e.o
  "___cxa_begin_catch", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
      ___clang_call_terminate in my-82a25e.o
  "___cxa_end_catch", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
  "___gxx_personality_v0", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in my-82a25e.o
      std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> > std::__1::__pad_and_output<char, std::__1::char_traits<char> >(std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> >, char const*, char const*, char const*, std::__1::ios_base&, char) in my-82a25e.o
      Dwarf Exception Unwind Info (__eh_frame) in my-82a25e.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

It failed to link with clang because clang is intended to be used as a C compiler. This tradition--if you can call it that--comes from GCC, whose command-line interface clang follows. If you invoke GCC as g++ or Clang as clang++, it will automatically understand that it is to compile C++ code, and it will automatically link in the C++ standard library.

If you use the plain gcc or clang you can still compile C++ code, but to link it you will usually need to explicitly link the standard library (e.g. -lc++. It's easier and more conventional to just use the C++ oriented name when invoking the compiler.