libc/stdlib/strtod.3

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.Dd May 11, 2010
.Dt STRTOD 3
.Os
.Sh NAME
.Nm strtod , strtof , strtold
.Nd convert
.Tn ASCII
string to floating point
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft double
.Fn strtod "const char * restrict nptr" "char ** restrict endptr"
.Ft float
.Fn strtof "const char * restrict nptr" "char ** restrict endptr"
.Ft "long double"
.Fn strtold "const char * restrict nptr" "char ** restrict endptr"
.Sh DESCRIPTION
These conversion
functions convert the initial portion of the string
pointed to by
.Fa nptr
to
.Vt double ,
.Vt float ,
and
.Vt "long double"
representation, respectively.
.Pp
The expected form of the string is an optional plus (``+'') or minus
sign (``\-'') followed by either:
.Bl -bullet
.It
a decimal significand consisting of a sequence of decimal digits
optionally containing a decimal-point character, or
.It
a hexadecimal significand consisting of a ``0X'' or ``0x'' followed
by a sequence of hexadecimal digits optionally containing a
decimal-point character.
.El
.Pp
In both cases, the significand may be optionally followed by an
exponent.
An exponent consists of an ``E'' or ``e'' (for decimal
constants) or a ``P'' or ``p'' (for hexadecimal constants),
followed by an optional plus or minus sign, followed by a
sequence of decimal digits.
For decimal constants, the exponent indicates the power of 10 by
which the significand should be scaled.
For hexadecimal constants, the scaling is instead done by powers
of 2.
.Pp
Alternatively, if the portion of the string following the optional
plus or minus sign begins with
.Dq INFINITY
or
.Dq NAN ,
ignoring case, it is interpreted as an infinity or a quiet \*(Na,
respectively.
The syntax
.Dq Xo Pf NAN( Ar "s" ) Xc ,
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 white-space characters in the
string (as defined by the
.Xr isspace 3
function) are skipped.
The decimal point
character is defined in the program's locale (category
.Dv LC_NUMERIC ) .
.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 ,
.Dv HUGE_VALF ,
or
.Dv HUGE_VALL
is returned (according to the sign and type of the return 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 nan 3 ,
.Xr strtol 3 ,
.Xr strtoul 3 ,
.Xr wcstod 3
.Sh STANDARDS
The
.Fn strtod
function
conforms to
.St -isoC-99 .
.Sh AUTHORS
The author of this software is
.An David M. Gay .
.Bd -literal
Copyright (c) 1998 by Lucent Technologies
All Rights Reserved

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.Ed