strtod(3)		    Library Functions Manual		       strtod(3)

NAME
     strtod, strtof, strtold - convert ASCII string to floating-point number

LIBRARY
     Standard C library (libc, -lc)

SYNOPSIS
     #include <stdlib.h>

     double strtod(const char *restrict nptr,
		   char **_Nullable restrict endptr);
     float strtof(const char *restrict nptr,
		   char **_Nullable restrict endptr);
     long double strtold(const char *restrict nptr,
		   char **_Nullable restrict endptr);

 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

     strtof(), strtold():
	 _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION
     The strtod(), strtof(), and strtold() functions convert the initial portion
     of	 the  string pointed to by nptr to double, float, and long double repre-
     sentation, respectively.

     The expected form of the (initial portion of the) string is optional  lead-
     ing  white space as recognized by isspace(3), an optional plus ('+') or mi-
     nus 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  con-
     sists  of	an  'E' or 'e', followed by an optional plus or minus sign, fol-
     lowed by a nonempty sequence of decimal digits, and  indicates  multiplica-
     tion by a power of 10.

     A	hexadecimal number consists of a "0x" or "0X" followed by a nonempty se-
     quence of hexadecimal digits possibly containing a radix character, option-
     ally 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 se-
     quence 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-depen-
     dent way the type of NAN (see VERSIONS).

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.

ERRORS
     ERANGE
	    Overflow or underflow occurred.

ATTRIBUTES
     For an explanation of the terms used in this  section,  see  attributes(7).
     allbox; lbx lb lb l l l.  Interface Attribute Value T{ strtod(), strtof(),
     strtold() T}   Thread safety  MT-Safe locale

VERSIONS
     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 compo-
     nent of the returned value.

STANDARDS
     C11, POSIX.1-2008.

HISTORY
     strtod()
	    C89, POSIX.1-2001.

     strtof()
     strtold()
	    C99, POSIX.1-2001.

CAVEATS
     Since 0 can legitimately be returned on both success and failure, the call-
     ing 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.

EXAMPLES
     See  the example on the strtol(3) manual page; the use of the functions de-
     scribed in this manual page is similar.

SEE ALSO
     atof(3), atoi(3), atol(3),	 nan(3),  nanf(3),  nanl(3),  strfromd(3),  str-
     tol(3), strtoul(3)

Linux man-pages 6.18		   2025-05-17			       strtod(3)