STRTOD(3) | Library Functions Manual | STRTOD(3) |
strtod
, strtof
,
strtold
— convert ASCII
string to floating point
Standard C Library (libc, -lc)
#include
<stdlib.h>
double
strtod
(const char *restrict
nptr, char **restrict endptr);
float
strtof
(const char *restrict
nptr, char **restrict endptr);
long double
strtold
(const char *restrict
nptr, char **restrict endptr);
These conversion functions convert the initial portion of the string pointed to by nptr to double, float, and long double representation, respectively.
The expected form of the string is an optional plus (``+'') or minus (``-'') sign, followed by either:
In both cases, the significand may be optionally followed by an exponent. An exponent consists of an ``E'' or ``e'' (for decimal constants) or a ``P'' or ``p'' (for hexadecimal constants), followed by an optional plus or minus sign, followed by a sequence of decimal digits. For decimal constants, the exponent indicates the power of 10 by which the significand should be scaled. For hexadecimal constants, the scaling is instead done by powers of 2.
If the portion of the string following the optional plus or minus sign begins with “INFINITY” or “INF”, ignoring case, it is interpreted as an infinity.
If the portion of the string following the optional plus
or minus sign begins with “NAN”, ignoring case, it is
interpreted as a quiet NaN. The syntax
“NAN(s)”, where s
is an alphanumeric string, produces the same value as the call
nan
("s");
(respectively,
nanf
("s");
and
nanl
("s");.)
In any of the above cases, leading white-space characters in the
string (as defined by the isspace(3)
function) are skipped. The decimal point character is defined in the
program's locale (category LC_NUMERIC
).
Extended locale versions of these functions are documented in strtod_l(3). See xlocale(3) for more information.
The strtod
(),
strtof
(), and strtold
()
functions return the converted value, if any, rounded to the nearest
representable value of the corresponding type according to the rounding mode
currently in effect. See
fegetround(3) for more information
on rounding modes. If flush-to-zero behavior is enabled in the current
floating-point environment, the behavior is identical except that any
subnormal values that would be returned will instead be returned as the
correspondingly-signed zero.
If endptr is not
NULL
, a pointer to the character after the last
character used in the conversion is stored in the location referenced by
endptr.
If no conversion is performed, zero is returned and the value of nptr is stored in the location referenced by endptr.
The input is converted by first rounding the value to the
precision of the target type but allowing an unbounded exponent range. If
the resulting exponent is too large for the target type, overflow is deemed
to have occurred. Overflow is signalled by returning
HUGE_VAL
, HUGE_VALF
, or
HUGE_VALL
(according to the sign of the input and
type of the return value), and storing ERANGE
in
errno.
If the input string is not an explicit representation of zero and
the correctly-rounded result is a subnormal or zero value, then
ERANGE
is stored in errno to
indicate underflow has occurred.
ERANGE
]atof(3), atoi(3), atol(3), nan(3), strtod_l(3), strtol(3), strtoul(3), wcstod(3)
The strtod
() function conforms to
ISO/IEC 9899:1999
(“ISO C99”).
Copyright (c) 1998 by Lucent Technologies All Rights Reserved Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that the copyright notice and this permission notice and warranty disclaimer appear in supporting documentation, and that the name of Lucent or any of its entities not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. LUCENT DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL LUCENT OR ANY OF ITS ENTITIES BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
July 2, 2021 | macOS 14.6 |