|STRTONUM(3)||Library Functions Manual||STRTONUM(3)|
reliably convert string value to an integer
strtonum(const char *nptr,
long long minval, long long
maxval, const char **errstr);
strtonum() function converts the
string in nptr to a
strtonum() function was designed to
facilitate safe, robust programming and overcome the shortcomings of the
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 ‘
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,
stores an error string in *errstr indicating 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
success; this fact can be used to differentiate a successful return of 0
from an error.
strtonum() correctly is meant to be
simpler than the alternative functions.
int iterations; 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 64 (inclusive).
If an error occurs, errstr will be set to one of the following strings:
strtonum() function first appeared in
|February 7, 2016||OpenBSD-current|