strtod(3C)

NAME

strtod, atof — convert string to double-precision number

SYNOPSIS

#include <stdlib.h>

double strtod(const char *str, char **ptr);

double atof(const char *str);

DESCRIPTION

strtod() returns, as a double-precision floating-point number, the value represented by the character string pointed to by str. The string is scanned (leading white-space characters as defined by isspace() in ctype(3C) are ignored) up to the first unrecognized character. If no conversion can take place, zero is returned.

strtod() recognizes characters in the following sequence:

1.: An optional string of ``white-space'' characters which are ignored,
2.: An optional sign,
3.: A string of digits optionally containing a radix character,
4.: An optional e or E followed by an optional sign or space, followed by an integer.

The radix character is determined by the loaded NLS environment (see setlocale(3C)). If setlocale() has not been called successfully, the default NLS environment, "C", is used (see lang(5)). The default environment specifies a period (.) as the radix character.

If the value of ptr is not (char **)NULL, the variable to which it points is set to point at the character after the last number, if any, that was recognized. If no number can be formed, *ptr is set to str, and zero is returned.

atof(str) is equivalent to strtod (str, (char **)NULL).

EXTERNAL INFLUENCES

Locale

The LC_NUMERIC category determines the value of the radix character within the currently loaded NLS environment.

APPLICATION USAGE

strtod() and atof() are thread-safe and async-cancel-safe.

RETURN VALUE

If the correct value would cause overflow, +HUGE_VAL or -HUGE_VAL is returned (according to the sign of the value), and errno is set to ERANGE.

If the correct value would cause underflow, zero is returned and errno is set to ERANGE.

When the input parameter character string for strtod() and atof() is either inf (case insensitive) or infinity (case insensitive) strtod() and atof() will return HUGE_VAL.

When the input parameter character string for strtod() and atof() is nan (case insensitive), strtod() and atof() will return _DNANQ.

AUTHOR

strtod() was developed by AT&T and HP.

STANDARDS CONFORMANCE

strtod(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, ANSI C

atof(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C