| STRTONUM(3) | Library Functions Manual | STRTONUM(3) | 
strtonum —
#include
    <stdlib.h>
long long
  
  strtonum(const char *nptr,
    long long minval, long long
    maxval, const char **errstr);
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.
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.
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).
EINVAL]ERANGE]If an error occurs, errstr will be set to one of the following strings:
strtonum() is an OpenBSD
  extension.
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.
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:
strtonum()
  NetBSD provides
  strtou(3) and
  strtoi(3).
| January 18, 2015 | NetBSD 10.0 |