NAME
strtonum —
reliably convert string
value to an integer
SYNOPSIS
#define _OPENBSD_SOURCE
#include <stdlib.h>
long long
strtonum(
const char *nptr,
long long minval,
long long
maxval,
const char **errstr);
DESCRIPTION
The
strtonum() function converts the string in
nptr to a
long long
value.
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
long long
value according to base 10.
The value obtained is then checked against the provided
minval and
maxval bounds. If
errstr is non-null,
strtonum() stores
an error string in
*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
errstr will point to an error message.
*errstr will be set to
NULL
on
success; 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
-
-
- [
EINVAL
]
- The given string did not consist solely of digit
characters; or minval was larger than
maxval.
-
-
- [
ERANGE
]
- The given string was out of range.
If an error occurs,
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.
SEE ALSO
atof(3),
atoi(3),
atol(3),
atoll(3),
sscanf(3),
strtod(3),
strtoi(3),
strtol(3),
strtoll(3),
strtou(3),
strtoul(3),
strtoull(3)
STANDARDS
strtonum() is an
OpenBSD extension.
HISTORY
The
strtonum() function first appeared in
OpenBSD 3.6.
strtonum() was
redesigned in
NetBSD 8 as
strtoi(
3) and
strtou(
3). For compatibility reasons
it's available since
NetBSD 8 in the
_OPENBSD_SOURCE namespace.
CAVEATS
The
strtonum() function was designed to facilitate safe,
robust programming and overcome the shortcomings of the
atoi(3) and
strtol(3) family of interfaces,
however there are problems with the
strtonum() API:
- will return 0 on failure; 0 might not be in range, so that
necessitates an error check even if you want to avoid it
- does not differentiate 'illegal' returns, so we can't tell
the difference between partial and no conversions
- returns english strings
- can't set the base, or find where the conversion
ended
- hardcodes long long integer type
To overcome the shortcomings of
strtonum()
NetBSD provides
strtou(
3) and
strtoi(
3).