DragonFly On-Line Manual Pages
STRTOD(3) DragonFly Library Functions Manual STRTOD(3)
strtod, strtod_l, strtof, strtof_l, strtold, strtold_l -- convert ASCII
string to floating point
Standard C Library (libc, -lc)
strtod(const char * restrict nptr, char ** restrict endptr);
strtof(const char * restrict nptr, char ** restrict endptr);
strtold(const char * restrict nptr, char ** restrict endptr);
strtod_l(const char * restrict nptr, char ** restrict endptr,
strtof_l(const char * restrict nptr, char ** restrict endptr,
strtold_l(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,
The expected form of the string is an optional plus (``+'') or minus sign
(``-'') followed by either:
* a decimal significand consisting of a sequence of decimal digits
optionally containing a decimal-point character, or
* a hexadecimal significand consisting of a ``0X'' or ``0x'' followed
by a sequence of hexadecimal digits optionally containing a decimal-
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 signifi-
cand should be scaled. For hexadecimal constants, the scaling is instead
done by powers of 2.
Alternatively, if the portion of the string following the optional plus
or minus sign begins with ``INFINITY'' or ``NAN'', ignoring case, it is
interpreted as an infinity or a quiet NaN, respectively.
In any of the above cases, leading white-space characters in the string
(as defined by the isspace(3) or isspace_l(3) functions) are skipped.
The decimal point character is defined in the program's locale (category
The strtod_l(), strtof_l(), and strtold_l() functions take an explicit
locale argument, whereas the strtod(), strtof(), and strtold() functions
use the current global or per-thread locale.
The strtod(), strtod_l(), strtof(), strtof_l(), strtold(), and
strtold_l() functions return the converted value, if any.
If endptr is not NULL, a pointer to the character after the last charac-
ter used in the conversion is stored in the location referenced by
If no conversion is performed, zero is returned and the value of nptr is
stored in the location referenced by endptr.
If the correct value would cause overflow, plus or minus HUGE_VAL,
HUGE_VALF, or HUGE_VALL is returned (according to the sign and type of
the return value), and ERANGE is stored in errno. If the correct value
would cause underflow, zero is returned and ERANGE is stored in errno.
[ERANGE] Overflow or underflow occurred.
atof(3), atoi(3), atol(3), strtol(3), strtoul(3), wcstod(3), xlocale(3)
The strtod() function conforms to ISO/IEC 9899:1999 (``ISO C99''), with
the exception of the bug noted below.
The author of this software is David M. Gay.
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
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
These routines do not recognize the C99 ``NaN(...)'' syntax.
DragonFly 4.9 December 25, 2013 DragonFly 4.9