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.\" Copyright (c) 2004 Ted Unangst
.\" Copyright 2023 Oxide Computer Company
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.Dd August 19, 2023
.Dt STRTONUM 3C
.Os
.Sh NAME
.Nm strtonum ,
.Nm strtonumx
.Nd reliably convert string value to an integer
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.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
.Ft long long
.Fo strtonumx
.Fa "const char *nptr"
.Fa "long long minval"
.Fa "long long maxval"
.Fa "const char **errstr"
.Fa "int base"
.Fc
.Sh DESCRIPTION
The
.Fn strtonum
and
.Fn strtonumx
functions convert the string in
.Fa nptr
to a
.Li long long
value.
These functions were designed to facilitate safe, robust programming and
overcome the shortcomings of the
.Xr atoi 3C
and
.Xr strtol 3C
family of interfaces.
.Pp
The string may begin with an arbitrary amount of whitespace
.Pq as determined by Xr isspace 3C
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
.Pq for Fn strtonum
or the provided base
.Pq for Fn strtonumx .
.Pp
The value obtained is then checked against the provided
.Fa minval
and
.Fa maxval
bounds.
If
.Fa errstr
is non-null,
.Fn strtonum
and
.Fn strtonumx
store an error string in
.Fa errstr
indicating the failure.
.Pp
For
.Fn strtonumx
the value of
.Ar base
is interpreted in the same way as described in
.Xr strtoll 3C .
In particular, if the value of
.Ar base
is 0, then the expected form of
.Ar nptr
is that of a decimal constant, octal constant or hexadecimal constant, any of
which may be preceded by a + or - sign.
.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 != NULL)
	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
.Pq inclusive .
.Sh ERRORS
The
.Fn strtonum
and
.Fn strtonumx
functions will fail if:
.Bl -tag -width Er
.It Er ERANGE
The value to be returned falls outside of the specified range.
.It Er EINVAL
.Ar minval
was larger than
.Ar maxval .
.El
.Pp
The
.Fn strtonum
function will fail if:
.Bl -tag -width Er
.It Er EINVAL
The given string did not consist solely of digit characters.
.El
.Pp
The
.Fn strtonumx
function will fail if:
.Bl -tag -width Er
.It Er EINVAL
The specified base was invalid, or the given string did not consist solely of
characters which are valid in that base.
.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 characters valid in the specified base
.Pq or base 10 for Fn strtonum .
.It Qq unparsable; invalid base specified
The specified base was outside the permitted range.
.El
.Sh INTERFACE STABILITY
.Sy Committed .
.Sh MT-LEVEL
.Sy Safe .
.Sh SEE ALSO
.Xr atof 3C ,
.Xr atoi 3C ,
.Xr atol 3C ,
.Xr atoll 3C ,
.Xr sscanf 3C ,
.Xr strtod 3C ,
.Xr strtol 3C ,
.Xr strtoll 3C ,
.Xr strtoul 3C
.Sh STANDARDS
.Fn strtonum
is an
.Ox
extension.
The existing alternatives, such as
.Xr atoi 3C
and
.Xr strtol 3C ,
are either impossible or difficult to use safely.
.Pp
.Fn strtonumx
is an illumos extension.