Reference

strtonum(3)

reliably convert string value to an integer

NAME

strtonum, strtonumx – reliably convert string value to an integer

SYNOPSIS

#include <stdlib.h>

long long

strtonum(const char *nptr, long long minval, long long maxval, const char **errstr);

long long

strtonumx(const char *nptr, long long minval, long long maxval, const char **errstr, int base);

DESCRIPTION

The strtonum() and strtonumx() functions convert the string in nptr to a long long value. These functions were 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 long long value according to base 10 (for strtonum()) or the provided base (for strtonumx()).

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

For strtonumx() the value of base is interpreted in the same way as described in strtoll(3). In particular, if the value of base is 0, then the expected form of nptr is that of a decimal constant, octal constant or hexadecimal constant, any of which may be preceded by a + or - sign.

RETURN VALUES

The strtonum() and strtonumx() functions return 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() and strtonumx() 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 (for strtonum()), or characters which are valid in the given base (for strtonumx()).

[EINVAL]

The supplied 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 characters valid in the specified base (or base 10 for strtonum()).

"unparsable; invalid base specified"

The specified base was outside the permitted range.

SEE ALSO

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

STANDARDS

The 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 strtonum() function first appeared in OpenBSD 3.6. The strtonumx() function first appeared in illumos in 2023.

History