STRTOD
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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NAME
strtod, strtof, strtold - convert ASCII string to floating-point number
SYNOPSIS
#include <stdlib.h>
double strtod(const char *nptr, char **endptr);
float strtof(const char *nptr, char **endptr);
long double strtold(const char *nptr, char **endptr);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
strtof(),
strtold():
-
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
DESCRIPTION
The
strtod(),
strtof(),
and
strtold()
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 (initial portion of the) string is
optional leading white space as recognized by
isspace(3),
an optional plus (aq+aq) or minus sign (aq-aq) and then either
(i) a decimal number, or (ii) a hexadecimal number,
or (iii) an infinity, or (iv) a NAN (not-a-number).
A
decimal number
consists of a nonempty sequence of decimal digits
possibly containing a radix character (decimal point, locale-dependent,
usually aq.aq), optionally followed by a decimal exponent.
A decimal exponent consists of an aqEaq or aqeaq, followed by an
optional plus or minus sign, followed by a nonempty sequence of
decimal digits, and indicates multiplication by a power of 10.
A
hexadecimal number
consists of a "0x" or "0X" followed by a nonempty sequence of
hexadecimal digits possibly containing a radix character,
optionally followed by a binary exponent.
A binary exponent
consists of a aqPaq or aqpaq, followed by an optional
plus or minus sign, followed by a nonempty sequence of
decimal digits, and indicates multiplication by a power of 2.
At least one of radix character and binary exponent must be present.
An
infinity
is either "INF" or "INFINITY", disregarding case.
A
NAN
is "NAN" (disregarding case) optionally followed by a string,
(n-char-sequence),
where
n-char-sequence
specifies in an implementation-dependent
way the type of NAN (see NOTES).
RETURN VALUE
These functions return the converted value, if any.
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 (unless
endptr
is null) 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,
HUGE_VALL)
is returned (according to the sign of the value), and
ERANGE
is stored in
errno.
If the correct value would cause underflow, zero is
returned and
ERANGE
is stored in
errno.
ERRORS
- ERANGE
-
Overflow or underflow occurred.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
strtod(),
strtof(),
strtold()
| Thread safety | MT-Safe locale
|
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C99.
strtod()
was also described in C89.
NOTES
Since
0 can legitimately be returned
on both success and failure, the calling program should set
errno
to 0 before the call,
and then determine if an error occurred by checking whether
errno
has a nonzero value after the call.
In the glibc implementation, the
n-char-sequence
that optionally follows "NAN"
is interpreted as an integer number
(with an optional '0' or '0x' prefix to select base 8 or 16)
that is to be placed in the
mantissa component of the returned value.
EXAMPLE
See the example on the
strtol(3)
manual page;
the use of the functions described in this manual page is similar.
SEE ALSO
atof(3),
atoi(3),
atol(3),
nan(3),
nanf(3),
nanl(3),
strfromd(3),
strtol(3),
strtoul(3)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- EXAMPLE
-
- SEE ALSO
-
- COLOPHON
-
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- Running on 
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