Proposed resolution:

This wording is relative to N3936.

1. Change [string.conversions] p4+p6 as indicated:

   float stof(const string& str, size_t* idx = 0);
   double stod(const string& str, size_t* idx = 0);
   long double stold(const string& str, size_t* idx = 0);
   

   -4- Effects: the first twoThese functions call strtof(str.c_str(), ptr), strtod(str.c_str(), ptr), and the third function calls strtold(str.c_str(), ptr), respectively. Each function returns the converted result, if any. […]

   […]

   -6- Throws: invalid_argument if strtof, strtod, or strtold reports that no conversion could be performed. Throws out_of_range if strtof, strtod, or strtold sets errno to ERANGE or if the converted value is outside the range of representable values for the return type.

2. Change [string.conversions] p11+p13 as indicated:

   float stof(const wstring& str, size_t* idx = 0);
   double stod(const wstring& str, size_t* idx = 0);
   long double stold(const wstring& str, size_t* idx = 0);
   

   -11- Effects: the first twoThese functions call wcstof(str.c_str(), ptr), wcstod(str.c_str(), ptr), and the third function calls wcstold(str.c_str(), ptr), respectively. Each function returns the converted result, if any. […]

   […]

   -13- Throws: invalid_argument if wcstof, wcstod, or wcstold reports that no conversion could be performed. Throws out_of_range if wcstof, wcstod, or wcstold sets errno to ERANGE.