man strtonum (3): reliably convert string value to an integer

LIBRARY

Lb libbsd

SYNOPSIS

In limits.h In bsd/stdlib.h Ft long long Fo strtonum Fa const char *nptr Fa long long minval Fa long long maxval Fa const char **errstr Fc

DESCRIPTION

The Fn strtonum function converts the string in Fa nptr to a Vt long long value. The Fn strtonum function was designed to facilitate safe, robust programming and overcome the shortcomings of the atoi(3) and 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 `+' or `-' sign.

The remainder of the string is converted to a Vt long long value according to base 10.

The value obtained is then checked against the provided Fa minval and Fa maxval bounds. If Fa errstr is non-null, Fn strtonum stores an error string in Fa *errstr indicating the failure.

RETURN VALUES

The Fn 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 Fa errstr will point to an error message. On success, Fa *errstr will be set to NULL this fact can be used to differentiate a successful return of 0 from an error.

EXAMPLES

Using Fn 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

Bq Er ERANGE: The given string was out of range.
Bq Er EINVAL: The given string did not consist solely of digit characters.
Bq Er EINVAL: The supplied Fa minval was larger than Fa maxval .

If an error occurs, Fa 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.

STANDARDS

The Fn strtonum function is a BSD extension. The existing alternatives, such as atoi(3) and strtol(3), are either impossible or difficult to use safely.

HISTORY

The Fn strtonum function first appeared in Ox 3.6 .