double strtod( const char *str, char **endptr )

	- prototype in string.h

	- converts string str to a double value
	- stops reading at tfirst character that cannot be interpreted
	  as part of a double value, returning in *endptr
	- str must have format:

	  [ws][sn][ddd][.][ddd][fmt[sn]ddd]

	  where [ws]  = optional whitespace
		[sn]  = optional sign (+-)
		[ddd] = optional digits
		[fmt] = option e or E
		[.]   = optional decimal point