преобразовать строку ASCII в число с плавающей запятой (convert ASCII string to floating-point number)
Имя (Name)
strtod, strtof, strtold - convert ASCII string to floating-point
number
Синопсис (Synopsis)
#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);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
strtof(), strtold():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
Описание (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 ('+') 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).
Возвращаемое значение (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, or HUGE_VALL is returned (according to the
return type and sign of the value), and ERANGE is stored in
errno.
If the correct value would cause underflow, a value with
magnitude no larger than DBL_MIN, FLT_MIN, or LDBL_MIN is
returned and ERANGE is stored in errno.
Ошибки (Error)
ERANGE Overflow or underflow occurred.
Атрибуты (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 │
└───────────────────────────────┴───────────────┴────────────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, C99.
strtod() was also described in C89.
Примечание (Note)
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.
Примеры (Examples)
See the example on the strtol(3) manual page; the use of the
functions described in this manual page is similar.
Смотри также (See also)
atof(3), atoi(3), atol(3), nan(3), nanf(3), nanl(3), strfromd(3),
strtol(3), strtoul(3)
