.\" Copyright (c) 1990, 1991 The Regents of the University of California.
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.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
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.\"	$OpenBSD: strtod.3,v 1.19 2014/01/19 10:39:00 schwarze Exp $
.\"
.Dd $Mdocdate: January 19 2014 $
.Dt STRTOD 3
.Os
.Sh NAME
.Nm strtod ,
.Nm strtof ,
.Nm strtold
.Nd convert ASCII string to double, float or long double
.Sh SYNOPSIS
.In stdlib.h
.Ft double
.Fn strtod "const char *nptr" "char **endptr"
.Pp
.Ft float
.Fn strtof "const char *nptr" "char **endptr"
.Pp
.Ft long double
.Fn strtold "const char *nptr" "char **endptr"
.Sh DESCRIPTION
The
.Fn strtod
function converts the initial portion of the string pointed to by
.Fa nptr
to
.Li double
representation.
The
.Fn strtof
function converts the initial portion of the string pointed to by
.Fa nptr
to
.Li float
representation.
The
.Fn strtold
function converts the initial portion of the string pointed to by
.Fa nptr
to
.Li long double
representation.
.Pp
The expected form of the string is an optional plus
.Pq Ql +
or minus sign
.Pq Ql -
followed by a sequence of digits optionally containing
a decimal-point character, optionally followed by an exponent.
An exponent consists of an
.Sq E
or
.Sq e ,
followed by an optional plus or minus sign, followed by a sequence of digits.
.Pp
Alternatively, if the portion of the string following the optional
plus or minus sign begins with
.Dq INF
or
.Dq NAN ,
ignoring case, it is interpreted as an infinity or a quiet \*(Na,
respectively.
The syntax
.Dq NAN Ns Pq Ar s ,
where
.Ar s
is an alphanumeric string, produces the same value as the call
.Fo nan
.Qq Ar s Ns
.Fc
(respectively,
.Fo nanf
.Qq Ar s Ns
.Fc
and
.Fo nanl
.Qq Ar s Ns
.Fc . )
.Pp
In any of the above cases, leading whitespace characters in the
string (as defined by the
.Xr isspace 3
function) are skipped.
.Sh RETURN VALUES
The
.Fn strtod ,
.Fn strtof
and
.Fn strtold
functions return the converted value, if any.
.Pp
If
.Fa endptr
is not
.Dv NULL ,
a pointer to the character after the last character used
in the conversion is stored in the location referenced by
.Fa endptr .
.Pp
If no conversion is performed, zero is returned and the value of
.Fa nptr
is stored in the location referenced by
.Fa endptr .
.Pp
If the correct value would cause overflow, plus or minus
.Dv HUGE_VAL
is returned (according to the sign of the value), and
.Er ERANGE
is stored in
.Va errno .
If the correct value would cause underflow, zero is returned and
.Er ERANGE
is stored in
.Va errno .
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er ERANGE
Overflow or underflow occurred.
.El
.Sh SEE ALSO
.Xr atof 3 ,
.Xr atoi 3 ,
.Xr atol 3 ,
.Xr strtol 3 ,
.Xr strtoul 3
.Sh STANDARDS
The
.Fn strtod
function conforms to
.St -ansiC-89 .
The
.Fn strtof
and
.Fn strtold
functions conform to
.St -ansiC-99 .