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atof(3)
NAME
  atof, strtod, strtof, strtold - Converts a character string to a double-
  precision floating-point value

SYNOPSIS
  #include <stdlib.h>

  double atof(
	  const char *nptr );

  double strtod(
	  const char *nptr,
	  char **endptr );

  float strtof(
	  const char *nptr,
	  char **endptr );

  long double strtold(
	  const char *nptr,
	  char **endptr );

LIBRARY
  Standard C Library (libc)

PARAMETERS
  nptr
      Points to the character string to convert.

  endptr
      Specifies either a null value, a pointer to the character that ended
      the scan, or a pointer to a null value.

DESCRIPTION
  The atof() function converts, to a double floating-point value, the string
  pointed to by the nptr parameter - up to the first character that is
  inconsistent with the format of a floating-point number. Leading space
  characters are ignored. A call to this function is equivalent to a call to
  strtod(nptr, (char **) NULL), except for error handling. When the value
  cannot be represented, the result is undefined.

  The strtod(), strtof(), and strtold() functions convert the initial portion
  of the string pointed to by the nptr parameter to double, float, and long
  double representation, respectively.	First, the input string is decomposed
  into the following three parts:

    ·  An initial, possibly empty, sequence of space characters (as specified
       by the isspace() function).

    ·  A subject sequence interpreted as a floating-point constant.

    ·  A final string of one or more unrecognized characters, including the
       terminating null character of the input string.

  After decomposition of the string, the subject sequence is converted to a
  floating-point number and the resulting value is returned. A subject
  sequence is defined as the longest initial subsequence of the input string,
  starting with the first non-space character, that is of the expected form.
  The expected form and order of the subject sequence is:

    ·  An optional plus (+) or minus (-) sign.

    ·  A sequence of digits optionally containing a radix character.

    ·  An optional exponent part. An exponent part consists of e or E,
       followed by an optional sign, which is followed by one or more decimal
       digits.

  The subject sequence contains no characters when the input string is empty
  or consists entirely of space characters, or when the first non-space
  character is other than a sign, a digit, or a radix character.

  For the strtod(), strtof(), and strtold() functions, when the value of the
  endptr parameter is not (char**) NULL, a pointer to the character that
  terminated the scan is stored at *endptr.

  When a floating-point value cannot be formed, *endptr is set to nptr.

  The strings NaN ("not a number"), Inf, and Infinity (the case of the
  characters does not matter) are recognized as valid only when the program
  is compiled with the -ieee option.

NOTES
  The setlocale() function may affect the radix character used in the
  conversion result.

  AES Support Level:
      Full use

RETURN VALUES
  When the string is empty or begins with an unrecognized character, +0.0 is
  returned as the floating-point value.

  If the calling routine is compiled with IEEE floating point enabled (-ieee
  option), errno will be set to ERANGE if the conversion underflows to zero.
  Similarly, if the value overflows, ERANGE will be set and a properly signed
  infinity will be returned.

  If the calling routine is not compiled with IEEE floating point enabled,
  any underflow will cause errno to be set to ERANGE and a properly signed
  zero to be returned. An overflow will cause errno to be set to ERANGE and
  will return a properly signed DBL_MAX, FLOAT_MAX, or LDBL_MAX.

  Upon successful completion, all of the functions return the converted
  floating-point value.

ERRORS
  If the atof(), strtod(), strtof(), or strtold() function fails, errno may
  be set to the following value:

  [ERANGE]
      The input string is out of range (that is, the subject sequence cannot
      be converted to a floating-point value without causing underflow or
      overflow).

SEE ALSO
  Functions: atoi(3), scanf(3)

Index for Section 3

Alphabetical listing for A

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