8' number.

Syntax
     '__float128 strtoflt128 (const char *s, char **sp)'

_Arguments_:
     S           input string
     SP          the address of the next character in the string

     The argument SP contains, if not 'NULL', the address of the next
     character following the parts of the string, which have been read.

Example
          #include <quadmath.h>

          int main ()
          {
            __float128 r;

            r = strtoflt128 ("1.2345678", NULL);

            return 0;
          }