HP-UX Reference (11i v1 05/09) - 3 Library Functions N-Z (vol 7)

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strtod(3C) 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.

RETURN VALUE

If the correct value after rounding would cause overﬂow (greater in magnitude than MAXDOUBLE (see

values(5)), +HUGE_VAL or -HUGE_VAL is returned (according to the sign of the value), and errno

set to

ERANGE.

If the correct value after rounding would cause underﬂow (lesser in magnitude than MINDOUBLE (see

values(5)), 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), HUGE_VAL

is returned.

When the input parameter character string for

strtod() and atof() is nan (case insensitive, Not-a-

Number), a quiet NaN (QNaN) is returned.

AUTHOR

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