strtod, strtof, strtold - convert ASCII string to floating-point number
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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).
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.
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.
infinity is either "INF" or "INFINITY", disregarding
NAN is "NAN" (disregarding case) optionally followed by a
specifies in an implementation-dependent way the type of NAN (see
These functions return the converted value, if any.
endptr is not NULL, a pointer to the character after the
last character used in the conversion is stored in the location
If no conversion is performed, zero is returned and (unless
endptr is null) the value of
nptr is stored in the
location referenced by
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
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
See the example on the strtol(3) manual page; the use of the functions described in this manual page is similar.
Overflow or underflow occurred.
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
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.
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