xref: /netbsd-src/lib/libc/stdlib/strtonum.3 (revision 194f011f43c9d4da6dad3d29585a591ae3ed1ea2)

.\" $NetBSD: strtonum.3,v 1.2 2015/01/19 11:47:41 wiz Exp $
.\" $OpenBSD: strtonum.3,v 1.17 2013/08/14 06:32:28 jmc Exp $
.\"
.\" Copyright (c) 2004 Ted Unangst
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd January 18, 2015
.Dt STRTONUM 3
.Os
.Sh NAME
.Nm strtonum
.Nd reliably convert string value to an integer
.Sh SYNOPSIS
.Vt #define _OPENBSD_SOURCE
.In stdlib.h
.Ft long long
.Fo strtonum
.Fa "const char *nptr"
.Fa "long long minval"
.Fa "long long maxval"
.Fa "const char **errstr"
.Fc
.Sh DESCRIPTION
The
.Fn strtonum
function converts the string in
.Fa nptr
to a
.Li long long
value.
.Pp
The string may begin with an arbitrary amount of whitespace
(as determined by
.Xr isspace 3 )
followed by a single optional
.Ql +
or
.Ql -
sign.
.Pp
The remainder of the string is converted to a
.Li long long
value according to base 10.
.Pp
The value obtained is then checked against the provided
.Fa minval
and
.Fa maxval
bounds.
If
.Fa errstr
is non-null,
.Fn strtonum
stores an error string in
.Fa *errstr
indicating the failure.
.Sh RETURN VALUES
The
.Fn strtonum
function returns the result of the conversion,
unless the value would exceed the provided bounds or is invalid.
On error, 0 is returned,
.Va errno
is set, and
.Fa errstr
will point to an error message.
.Fa *errstr
will be set to
.Dv NULL
on success;
this fact can be used to differentiate
a successful return of 0 from an error.
.Sh EXAMPLES
Using
.Fn strtonum
correctly is meant to be simpler than the alternative functions.
.Bd -literal -offset indent
int iterations;
const char *errstr;

iterations = strtonum(optarg, 1, 64, &errstr);
if (errstr)
	errx(1, "number of iterations is %s: %s", errstr, optarg);
.Ed
.Pp
The above example will guarantee that the value of iterations is between
1 and 64 (inclusive).
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
The given string did not consist solely of digit characters; or
.Ar minval
was larger than
.Ar maxval .
.It Bq Er ERANGE
The given string was out of range.
.El
.Pp
If an error occurs,
.Fa errstr
will be set to one of the following strings:
.Pp
.Bl -tag -width "too largeXX" -compact
.It Qq too large
The result was larger than the provided maximum value.
.It Qq too small
The result was smaller than the provided minimum value.
.It Qq invalid
The string did not consist solely of digit characters.
.El
.Sh SEE ALSO
.Xr atof 3 ,
.Xr atoi 3 ,
.Xr atol 3 ,
.Xr atoll 3 ,
.Xr sscanf 3 ,
.Xr strtod 3 ,
.Xr strtoi 3 ,
.Xr strtol 3 ,
.Xr strtoll 3 ,
.Xr strtou 3 ,
.Xr strtoul 3 ,
.Xr strtoull 3
.Sh STANDARDS
.Fn strtonum
is an
.Ox
extension.
.Sh HISTORY
The
.Fn strtonum
function first appeared in
.Ox 3.6 .
.Fn strtonum
was redesigned in
.Nx 8
as
.Fn strtoi 3
and
.Fn strtou 3 .
For compatibility reasons it's available since
.Nx 8
in the
.Vt _OPENBSD_SOURCE
namespace.
.Sh CAVEATS
The
.Fn strtonum
function was designed to facilitate safe,
robust programming and overcome the shortcomings of the
.Xr atoi 3
and
.Xr strtol 3
family of interfaces, however there are problems with the
.Fn strtonum
API:
.Bl -dash
.It
will return 0 on failure; 0 might not be in range, so that necessitates
an error check even if you want to avoid it
.It
does not differentiate 'illegal' returns, so we can't tell the
difference between partial and no conversions
.It
returns english strings
.It
can't set the base, or find where the conversion ended
.It
hardcodes long long integer type
.El
To overcome the shortcomings of
.Fn strtonum
.Nx
provides
.Fn strtou 3
and
.Fn strtoi 3 .