strtod, strtof, strtold - convert ASCII string to floating-point number
#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
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 ('+') or
minus sign ('-') 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 '.'), optionally followed by a decimal exponent. A decimal exponent
consists of an 'E' or 'e', 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 'P' or 'p', 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).
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.
- ERANGE
- Overflow or underflow occurred.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| strtod (), strtof (), strtold () |
Thread safety |
MT-Safe locale |
POSIX.1-2001, POSIX.1-2008, C99.
strtod() was also described in C89.
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.
See the example on the
strtol(3) manual page; the use of the functions
described in this manual page is similar.
atof(3),
atoi(3),
atol(3),
nan(3),
nanf(3),
nanl(3),
strfromd(3),
strtol(3),
strtoul(3)