strtod, strtof—string to double or float #include <stdlib.h>
double strtod(const char *restrict str, char **restrict tail);
float strtof(const char *restrict str, char **restrict tail);
double _strtod_r(void *reent,
const char *restrict str, char **restrict tail);
Description
The function strtod parses the character string str,
producing a substring which can be converted to a double
value. The substring converted is the longest initial
subsequence of str, beginning with the first
non-whitespace character, that has one of these formats:
[+|-]digits[.[digits]][(e|E)[+|-]digits]
[+|-].digits[(e|E)[+|-]digits]
[+|-](i|I)(n|N)(f|F)[(i|I)(n|N)(i|I)(t|T)(y|Y)]
[+|-](n|N)(a|A)(n|N)[<(>[hexdigits]<)>]
[+|-]0(x|X)hexdigits[.[hexdigits]][(p|P)[+|-]digits]
[+|-]0(x|X).hexdigits[(p|P)[+|-]digits]
The substring contains no characters if str is empty, consists
entirely of whitespace, or if the first non-whitespace
character is something other than +, -, ., or a
digit, and cannot be parsed as infinity or NaN. If the platform
does not support NaN, then NaN is treated as an empty substring.
If the substring is empty, no conversion is done, and
the value of str is stored in *tail. Otherwise,
the substring is converted, and a pointer to the final string
(which will contain at least the terminating null character of
str) is stored in *tail. If you want no
assignment to *tail, pass a null pointer as tail.
strtof is identical to strtod except for its return type.
This implementation returns the nearest machine number to the
input decimal string. Ties are broken by using the IEEE
round-even rule. However, strtof is currently subject to
double rounding errors.
The alternate function _strtod_r is a reentrant version.
The extra argument reent is a pointer to a reentrancy structure.
Returns
strtod returns the converted substring value, if any. If
no conversion could be performed, 0 is returned. If the
correct value is out of the range of representable values,
plus or minus HUGE_VAL is returned, and ERANGE is
stored in errno. If the correct value would cause underflow, 0
is returned and ERANGE is stored in errno.
Supporting OS subroutines required: close, fstat, isatty,
lseek, read, sbrk, write.