NAME¶
strtonum
—
reliably convert string value to an integer
LIBRARY¶
library “libbsd”
SYNOPSIS¶
#include
<limits.h>
#include
<bsd/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
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
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. On success,
*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¶
- [
ERANGE
]
- The given string was out of range.
- [
EINVAL
]
- The given string did not consist solely of digit characters.
- [
EINVAL
]
- The supplied minval was larger than
maxval.
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),
strtol(3),
strtoul(3)
STANDARDS¶
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
OpenBSD 3.6.