$ cat test.cpp
#include <iostream>

struct S {
  unsigned Offset;
};

int main() {
  S s;
  std::cerr << s.Offset << std::endl;
}
$ clang++ -g -O0 -o test test.cpp
$ valgrind ./test
==31013== Memcheck, a memory error detector
==31013== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==31013== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==31013== Command: ./test
==31013== 
==31013== Use of uninitialised value of size 8
==31013==    at 0x4F39263: ??? (in /usr/lib64/libstdc++.so.6.0.21)
==31013==    by 0x4F3A84C: std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_int<unsigned long>(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, unsigned long) const (in /usr/lib64/libstdc++.so.6.0.21)
==31013==    by 0x4F3A9EC: std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::do_put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, unsigned long) const (in /usr/lib64/libstdc++.so.6.0.21)
==31013==    by 0x4F465B9: std::ostream& std::ostream::_M_insert<unsigned long>(unsigned long) (in /usr/lib64/libstdc++.so.6.0.21)
==31013==    by 0x400909: main (test.cpp:9)
==31013== 
==31013== Conditional jump or move depends on uninitialised value(s)
==31013==    at 0x4F3926F: ??? (in /usr/lib64/libstdc++.so.6.0.21)
==31013==    by 0x4F3A84C: std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_int<unsigned long>(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, unsigned long) const (in /usr/lib64/libstdc++.so.6.0.21)
==31013==    by 0x4F3A9EC: std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::do_put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, unsigned long) const (in /usr/lib64/libstdc++.so.6.0.21)
==31013==    by 0x4F465B9: std::ostream& std::ostream::_M_insert<unsigned long>(unsigned long) (in /usr/lib64/libstdc++.so.6.0.21)
==31013==    by 0x400909: main (test.cpp:9)
==31013== 
0
==31013== 
==31013== HEAP SUMMARY:
==31013==     in use at exit: 72,704 bytes in 1 blocks
==31013==   total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==31013== 
==31013== LEAK SUMMARY:
==31013==    definitely lost: 0 bytes in 0 blocks
==31013==    indirectly lost: 0 bytes in 0 blocks
==31013==      possibly lost: 0 bytes in 0 blocks
==31013==    still reachable: 72,704 bytes in 1 blocks
==31013==         suppressed: 0 bytes in 0 blocks
==31013== Rerun with --leak-check=full to see details of leaked memory
==31013== 
==31013== For counts of detected and suppressed errors, rerun with: -v
==31013== Use --track-origins=yes to see where uninitialised values come from
==31013== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)