STRTONUM(3C) Standard C Library Functions STRTONUM(3C)

NAME

strtonum - reliably convert string value to an integer

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <stdlib.h>

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 strtonum() function was designed to facilitate safe, robust programming
and overcome the shortcomings of the atoi(3C) and strtol(3C) family of
interfaces.

The string may begin with an arbitrary amount of whitespace (as determined
by isspace(3C)) 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. errstr
will be set to NULL on success; 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 != 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).

ERRORS

ERANGE The given string was out of range.

EINVAL The given string did not consist solely of digit
characters.

EINVAL minval was larger than maxval.

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.

INTERFACE STABILITY

Committed.

MT-LEVEL
Safe.

SEE ALSO

atof(3C), atoi(3C), atol(3C), atoll(3C), sscanf(3C), strtod(3C),
strtol(3C), strtoul(3C)

STANDARDS

strtonum() is an OpenBSD extension. The existing alternatives, such as
atoi(3C) and strtol(3C), are either impossible or difficult to use safely.

OmniOS February 7, 2016 OmniOS