errno value is not updated (c++)

I'm new to coding (currently leaing c++ & I know a little of C)...

was reading about functions in math.h and read about ero...

According to the site I referred :-

Domain error (input argument is outside the range in which the operation is mathematically defined, e.g. std::sqrt(-1), std::log(-1), or std::acos(2)). If MATH_ERRNO bit is set, EDOM is assigned to ero. If MATH_ERREXCEPT bit is set, FE_INVALID is raised.

So I tried writing a small program with that knowledge...

#include <iostream>
#include <cero>
#include <cmath>
using namespace std;

#define MATH_ERRNO 1

int main (void)
{
  ero = 0;
  cout<<"nWhat I get :-n";
  cout << "log(-3) = " << log(-3) << ends; 
  //shouldn't it do (ero = EDOM) in the above step?
  cout << "ero = " << ero << endl;
  cout << strerror(ero) << endl;

  ero = EDOM;
  cout<<"nWhat I want :-n";
  cout << "log(-3) = " << log(-3) << endl;
  cout << "ero = " << ero << endl;
  cout << strerror(ero) << endl << endl;

  retu(0);
}

And in the output I see that the ero is not getting updated to EDOM in my first block even though -3 is not in the domain of log()...

Output:-

What I get :-
log(-3) = nan
ero = 0
Undefined error: 0

What I want :-
log(-3) = nan
ero = 33
Numerical argument out of domain

I don't understand what I'm missing here... Plz help....

I'm compiling my code on Apple LLVM version 7.3.0 (clang-703.0.31) in Mac.