cet-is » cetlib

Building cetlib on macOS (El Cap, Xcode 7, 8), a tautological compare warning (promoted to error by CET default flags) is emitted by cetlib::ston specialised on unsigned

[ 65%] Building CXX object cetlib/test/CMakeFiles/ston_test.dir/ston_test.cc.o
In file included from /.../cetlib/test/ston_test.cc:4:
/.../cetlib/ston.h:90:17: error: comparison of unsigned expression < 0 is always false
      [-Wtautological-compare]
  if(    result < std::numeric_limits<unsigned>::min()
         ~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Clang clearly has higher default warnings than GCC, but I think this is valid as the code block in question is:

template<>
unsigned
  cet::ston<unsigned>( std::string s )
{
  std::size_t size;
  unsigned long result = stoul(s, &size);
  if( size < s.size() )
    throw std::invalid_argument("ston<unsigned long>");
  if(    result < std::numeric_limits<unsigned>::min()
      || std::numeric_limits<unsigned>::max() < result
    )
    throw std::out_of_range("ston<unsigned long>");
  return static_cast<unsigned>(result);
}

result is defined as unsigned long, so I think that guarantees it to have the same min value as unsigned, i.e. zero. Changing the code to

template<>
unsigned
  cet::ston<unsigned>( std::string s )
{
  std::size_t size;
  unsigned long result = stoul(s, &size);
  if( size < s.size() )
    throw std::invalid_argument("ston<unsigned long>");
  if( std::numeric_limits<unsigned>::max() < result )
    throw std::out_of_range("ston<unsigned long>");
  return static_cast<unsigned>(result);
}

has the same behaviour. At least, it compiles and passes the tests.