NAME
strtod, atof — convert string to double-precision number
SYNOPSIS
#include <stdlib.h>
double strtod(const char *str, char **ptr);
double atof(const char *str);
DESCRIPTION
strtod()
returns, as a double-precision floating-point number,
the value represented by the character string pointed to by
str.
The string is scanned (leading white-space characters as defined by
isspace()
in
ctype(3C)
are ignored) up to the first unrecognized character.
If no conversion can take place, zero is returned.
strtod()
recognizes characters in the following sequence:
- 1.
An optional string of ``white-space'' characters which are ignored,
- 2.
An optional sign,
- 3.
A string of digits optionally containing a radix character,
- 4.
An optional
e
or
E
followed by an optional sign or space, followed by an integer.
The radix character is determined by the loaded
NLS
environment (see
setlocale(3C)).
If
setlocale()
has not been called successfully, the default
NLS
environment, "C", is used (see
lang(5)).
The default environment specifies a period
(.)
as the radix character.
If the value of
ptr
is not
(char **)NULL,
the variable to which it points
is set to point at the character after the last number,
if any, that was recognized.
If no number can be formed,
*ptr
is set to
str,
and zero is returned.
atof(str)
is equivalent to
strtod (str, (char **)NULL).
EXTERNAL INFLUENCES
Locale
The
LC_NUMERIC
category determines the value of the radix character
within the currently loaded
NLS
environment.
APPLICATION USAGE
strtod()
and
atof()
are thread-safe and async-cancel-safe.
RETURN VALUE
If the correct value after rounding would cause overflow
(greater in magnitude than MAXDOUBLE (see
values(5)),
+HUGE_VAL
or
-HUGE_VAL
is returned (according to the sign of the value), and
errno
is set to
ERANGE.
If the correct value after rounding would cause underflow
(lesser in magnitude than MINDOUBLE (see
values(5)),
zero is returned and
errno
is set to
ERANGE.
When the input parameter character string for
strtod()
and
atof()
is either
inf
(case insensitive) or
infinity
(case insensitive),
HUGE_VAL
is returned.
When the input parameter character string for
strtod()
and
atof()
is
nan
(case insensitive, Not-a-Number),
a quiet
NaN
(QNaN)
is returned.
AUTHOR
strtod()
was developed by AT&T and HP.
STANDARDS CONFORMANCE
strtod(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, ANSI C
atof(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C
Printable version
