NAME
strtonum —
reliably convert string value to an
integer
LIBRARY
library “libc”
SYNOPSIS
#include
<stdlib.h>
long long
strtonum(const char *nptr,
long long minval, long long
maxval, const char **errstr);
DESCRIPTION
Thestrtonum()
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.
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) 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.
SEE ALSO
atof(3), atoi(3), atol(3), atoll(3), sscanf(3), strtod(3), strtol(3), strtoul(3)
STANDARDS
strtonum() was originally implemented as
an extension on OpenBSD. The existing alternatives,
such as atoi(3) and
strtol(3) are either impossible or difficult to use safely.