reliably convert string value to an integer
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
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. On success,
*errstr will be set to
this fact can be used to differentiate a successful return of 0 from an
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).
- The given string did not consist solely of digit characters; or minval was larger than maxval.
- The given string was out of range.
If an error occurs, errstr will be set to one of the following strings:
strtonum() is an
strtonum() function first appeared in
redesigned in NetBSD 8.0 as
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
- 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
strtonum() NetBSD provides
|January 18, 2015||Debian|