.\" $OpenBSD: ecvt.3,v 1.11 2013/06/05 03:39:23 tedu Exp $
.\"
.\" Copyright (c) 2002 Todd C. Miller <Todd.Miller@courtesan.com>
.\"
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.\"
.Dd $Mdocdate: June 5 2013 $
.Dt ECVT 3
.Os
.Sh NAME
.Nm ecvt ,
.Nm fcvt ,
.Nm gcvt
.Nd convert double to
.Tn ASCII
string
.Sh SYNOPSIS
.In stdlib.h
.Ft char *
.Fn ecvt "double value" "int ndigit" "int *decpt" "int *sign"
.Ft char *
.Fn fcvt "double value" "int ndigit" "int *decpt" "int *sign"
.Ft char *
.Fn gcvt "double value" "int ndigit" "char *buf"
.Sh DESCRIPTION
.Bf -symbolic
These functions are provided for compatibility with legacy code.
New code should use the
.Xr snprintf 3
function for improved safety and portability.
.Ef
.Pp
The
.Fn ecvt ,
.Fn fcvt
and
.Fn gcvt
functions convert the double precision floating-point number
.Fa value
to a NUL-terminated
.Tn ASCII
string.
.Pp
The
.Fn ecvt
function converts
.Fa value
to a NUL-terminated string of exactly
.Fa ndigit
digits and returns a pointer to that string.
The result is padded with zeroes from left to right as needed.
There are no leading zeroes unless
.Fa value
itself is 0.
The least significant digit is rounded in an implementation-dependent manner.
The position of the decimal point relative to the beginning of the string
is stored in
.Fa decpt .
A negative value indicates that the decimal point is located
to the left of the returned digits (this occurs when there is no
whole number component to
.Fa value ) .
If
.Fa value
is zero, it is unspecified whether the integer pointed to by
.Fa decpt
will be 0 or 1.
The decimal point itself is not included in the returned string.
If the sign of the result is negative, the integer pointed to by
.Fa sign
is non-zero; otherwise, it is 0.
.Pp
If the converted value is out of range or is not representable,
the contents of the returned string are unspecified.
.Pp
The
.Fn fcvt
function is identical to
.Fn ecvt
with the exception that
.Fa ndigit
specifies the number of digits after the decimal point (zero-padded as
needed).
.Pp
The
.Fn gcvt
function converts
.Fa value
to a NUL-terminated string similar to the %g
.Xr printf 3
format specifier and stores the result in
.Fa buf .
It produces
.Fa ndigit
significant digits similar to the %f
.Xr printf 3
format specifier where possible.
If
.Fa ndigit
does allow sufficient precision, the result is stored in
exponential notation similar to the %e
.Xr printf 3
format specifier.
If
.Fa value
is less than zero,
.Fa buf
will be prefixed with a minus sign.
A decimal point is included in the returned string if
.Fa value
is not a whole number.
Unlike the
.Fn ecvt
and
.Fn fcvt
functions,
.Fa buf
is not zero-padded.
.Sh RETURN VALUES
The
.Fn ecvt ,
.Fn fcvt
and
.Fn gcvt
functions return a NUL-terminated string representation of
.Fa value .
.Sh SEE ALSO
.Xr printf 3 ,
.Xr strtod 3
.Sh STANDARDS
The
.Fn ecvt ,
.Fn fcvt
and
.Fn gcvt
functions conform to
.St -p1003.1-2001 ;
as of
.St -p1003.1-2008
they are no longer a part of the standard.
.Sh CAVEATS
The
.Fn ecvt
and
.Fn fcvt
functions return a pointer to internal storage space that will be
overwritten by subsequent calls to either function.
.Pp
The maximum possible precision of the return value is limited by the
precision of a double and may not be the same on all architectures.
.Pp
The
.Xr snprintf 3
function is preferred over these functions for new code.