Cygwin gcc c++ c99 libraries error stod not recognized used strtod instead

Cygwin gcc c++ c99 libraries error stod not recognized used strtod instead

This question follows on from : c++ reading in text file into
vector<vector> then writing to vector or array depending on first word in
internal vector . Im editing this question because the first issue was
simply a typo error (couldn't ask seperate becaus eIve tried that before
and gow down voted for duplicate??, also couldnt delete Q because has
answers..), and the more important question is about the cygwin c++
compiler not having access to c99 libraries. When using stod instead of
strtod i get an compilation error. The issue is _GLIB_CXX_USE_C99 is
undefined??
Code so far:
#include <algorithm>
#include <fstream>
#include <iostream>
#include <iterator>
#include <sstream>
#include <string>
#include <vector>
#include <cstdlib>
#if __cplusplus < 201103L
#warning No C++11 support