NAME

     strtonum — reliably convert string value to an integer

LIBRARY

     Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS

     #include <limits.h>
     #include <stdlib.h>
     (See libbsd(7) for include usage.)

     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 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

     [EINVAL]           The given string did not consist solely of digit characters; or minval
                        was larger than maxval.

     [ERANGE]           The given string was out of range.

     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), strtoi(3bsd), strtol(3),
     strtoll(3), strtou(3bsd), strtoul(3), strtoull(3)

STANDARDS

     strtonum() is an OpenBSD extension.

HISTORY

     The strtonum() function first appeared in OpenBSD 3.6.  strtonum() was redesigned in
     NetBSD 8.0 as strtoi(3bsd) and strtou(3bsd).

CAVEATS

     The 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:

     -   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
     To overcome the shortcomings of strtonum() NetBSD provides strtou(3bsd) and strtoi(3bsd).