reliably convert string value to an integer
, long long minval
long long maxval
const char **errstr
() function converts the string in
value. The strtonum
() function was designed to
facilitate safe, robust programming and overcome the shortcomings of the
family of interfaces.
The string may begin with an arbitrary amount of whitespace (as determined by
) followed by a
single optional ‘
The remainder of the string is converted to a
value according to base 10.
The value obtained is then checked against the provided
() stores an error string in
indicating the failure.
() 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
will point to an error message.
will be set to
on success; this fact can be used to
differentiate a successful return of 0 from an error.
() correctly is meant to be simpler
than the alternative functions.
const char *errstr;
iterations = strtonum(optarg, 1, 64, &errstr);
if (errstr != NULL)
errx(1, "number of iterations is %s: %s", errstr, optarg);
The above example will guarantee that the value of iterations is between 1 and
- The given string was out of range.
- The given string did not consist solely of digit
- minval was larger than
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
- The string did not consist solely of digit characters.
() is an OpenBSD
extension. The existing alternatives, such as
, are either impossible
or difficult to use safely.
() function first appeared in