
STRTOD(3) Library functions STRTOD(3)
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);
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 (notanumber).
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 indi
cates 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 multiplica
tion 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 sequence of characters,
followed by ')'. The character string specifies in an implementationdependent way the
type of NAN.
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 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.
CONFORMING TO
ANSI C describes strtod, C99 describes the other two functions.
SEE ALSO
atof(3), atoi(3), atol(3), strtol(3), strtoul(3)
Linux 20010607 STRTOD(3) 
