STRTOD(3)                  Library Functions Manual                  STRTOD(3)

NAME
     strtod, strtof, strtold – convert ASCII string to floating point

LIBRARY
     Standard C Library (libc, -lc)

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);

DESCRIPTION
     These conversion 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 string is an optional plus (``+'') or minus
     (``-'') sign, followed by either:

     •   a decimal significand, consisting of a sequence of decimal digits
         (optionally containing a decimal-point character) or

     •   a hexadecimal significand, consisting of a ``0X'' or ``0x'' followed
         by a sequence of hexadecimal digits (optionally containing a decimal-
         point character).

     In both cases, the significand may be optionally followed by an exponent.
     An exponent consists of an ``E'' or ``e'' (for decimal constants) or a
     ``P'' or ``p'' (for hexadecimal constants), followed by an optional plus
     or minus sign, followed by a sequence of decimal digits.  For decimal
     constants, the exponent indicates the power of 10 by which the
     significand should be scaled.  For hexadecimal constants, the scaling is
     instead done by powers of 2.

     If the portion of the string following the optional plus or minus sign
     begins with “INFINITY” or “INF”, ignoring case, it is interpreted as an
     infinity.

     If the portion of the string following the optional plus or minus sign
     begins with “NAN”, ignoring case, it is interpreted as a quiet NaN.  The
     syntax “NAN(s)”, where s is an alphanumeric string, produces the same
     value as the call nan("s") (respectively, nanf("s") and nanl("s").)

     In any of the above cases, leading white-space characters in the string
     (as defined by the isspace(3) function) are skipped.  The decimal point
     character is defined in the program's locale (category LC_NUMERIC).

     Extended locale versions of these functions are documented in
     strtod_l(3).  See xlocale(3) for more information.

RETURN VALUES
     The strtod(), strtof(), and strtold() functions return the converted
     value, if any, rounded to the nearest representable value of the
     corresponding type according to the rounding mode currently in effect.
     See fegetround(3) for more information on rounding modes.  If flush-to-
     zero behavior is enabled in the current floating-point environment, the
     behavior is identical except that any subnormal values that would be
     returned will instead be returned as the correspondingly-signed zero.

     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.

     The input is converted by first rounding the value to the precision of
     the target type but allowing an unbounded exponent range.  If the
     resulting exponent is too large for the target type, overflow is deemed
     to have occurred.  Overflow is signalled by returning HUGE_VAL,
     HUGE_VALF, or HUGE_VALL (according to the sign of the input and type of
     the return value), and storing ERANGE in errno.

     If the input string is not an explicit representation of zero and the
     correctly-rounded result is a subnormal or zero value, then ERANGE is
     stored in errno to indicate underflow has occurred.

ERRORS
     [ERANGE]           Overflow or underflow occurred.

SEE ALSO
     atof(3), atoi(3), atol(3), nan(3), strtod_l(3), strtol(3), strtoul(3),
     wcstod(3)

STANDARDS
     The strtod() function conforms to ISO/IEC 9899:1999 (“ISO C99”).

     Copyright (c) 1998 by Lucent Technologies
     All Rights Reserved

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macOS 15.2                       July 2, 2021                       macOS 15.2