STRTONUM(3) | Library Functions Manual | STRTONUM(3) |
strtonum
—
reliably convert string value to an integer
#include
<stdlib.h>
long long
strtonum
(const char *nptr,
long long minval, long long
maxval, const char **errstr);
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(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.
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.
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.
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).
ERANGE
]EINVAL
]EINVAL
]If an error occurs, errstr will be set to one of the following strings:
atof(3), atoi(3), atol(3), atoll(3), sscanf(3), strtod(3), strtol(3), strtoul(3)
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.
The strtonum
() function first appeared in
OpenBSD 3.6.
April 29, 2004 | macOS 15.2 |