strtonum
- reliably convert string value to an integer
SYNOPSIS
#include <stdlib.h>
#include <limits.h> long long
Fo strtonum
Fa const char *nptr
Fa long long minval
Fa long long maxval
Fa const char **errstr
Fc
DESCRIPTION
The
strtonum ();
function converts the string in
Fa nptr
to a
Vt long long
value.
The
strtonum ();
function was designed to facilitate safe, robust programming
and overcome the shortcomings of the
atoi(3)
and
strtol(3)
family of interfaces.
The string may begin with an arbitrary amount of whitespace
(as determined by
isspace(3))
followed by a single optional
`+'
or
`-'
sign.
The remainder of the string is converted to a
Vt long long
value according to base 10.
The value obtained is then checked against the provided
Fa minval
and
Fa maxval
bounds.
If
Fa errstr
is non-null,
strtonum ();
stores an error string in
Fa *errstr
indicating the failure.
RETURN VALUES
The
strtonum ();
function returns the result of the conversion,
unless the value would exceed the provided bounds or is invalid.
On error, 0 is returned,
errno
is set, and
Fa errstr
will point to an error message.
On success,
Fa *errstr
will be set to
NULL
this fact can be used to differentiate
a successful return of 0 from an error.
EXAMPLES
Using
strtonum ();
correctly is meant to be simpler than the alternative functions.
int iterations;
const char *errstr;
iterations = strtonum(optarg, 1, 64, &errstr);
if (errstr)
errx(1, "number of iterations is %s: %s", errstr, optarg);
The above example will guarantee that the value of iterations is between
1 and 64 (inclusive).
ERRORS
Bq Er ERANGE
The given string was out of range.
Bq Er EINVAL
The given string did not consist solely of digit characters.
Bq Er EINVAL
The supplied
Fa minval
was larger than
Fa maxval .
If an error occurs,
Fa errstr
will be set to one of the following strings:
too large
The result was larger than the provided maximum value.
too small
The result was smaller than the provided minimum value.
invalid
The string did not consist solely of digit characters.
The
strtonum ();
function is a
BSD extension.
The existing alternatives, such as
atoi(3)
and
strtol(3),
are either impossible or difficult to use safely.
HISTORY
The
strtonum ();
function first appeared in
Ox 3.6 .
