NAME
strtou —
convert a string to an
uintmax_t integer
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <inttypes.h>
uintmax_t
strtou(
const char * restrict nptr,
char ** restrict endptr,
int base,
uintmax_t lo,
uintmax_t hi,
int *rstatus);
DESCRIPTION
The
strtou() function converts the string in
nptr to an
uintmax_t value. The
strtou() function uses internally
strtoumax(3) and ensures that
the result is always in the range [
lo ..
hi ]. In adddition it always places
0
on success or a conversion status in the
rstatus argument, avoiding the
errno
gymnastics the other functions require. The
rstatus argument can be
NULL
if
conversion status is to be ignored.
The string may begin with an arbitrary amount of white space (as determined by
isspace(3)) followed by a
single optional ‘
+
’ or
‘
-
’ sign. If
base is
zero or 16, the string may then include a
‘
0x
’ or
‘
0X
’ prefix, and the number will be read
in base 16; otherwise, a zero
base is taken as 10
(decimal) unless the next character is
‘
0
’, in which case it is taken as 8
(octal).
The remainder of the string is converted to an
uintmax_t value
in the obvious manner, stopping at the end of the string or at the first
character that does not produce a valid digit in the given base. (In bases
above 10, the letter ‘
A
’ in either upper
or lower case represents 10, ‘
B
’
represents 11, and so forth, with ‘
Z
’
representing 35.)
If
endptr is non-nil,
strtou() stores
the address of the first invalid character in
*endptr.
If there were no digits at all, however,
strtou() stores the
original value of
nptr in
*endptr.
(Thus, if
*nptr is not
‘
\0
’ but
**endptr is
‘
\0
’ on return, the entire string was
valid.)
RETURN VALUES
The
strtou() function always returns the closest value in the
range specified by the
lo and
hi
arguments.
The
errno value is guaranteed to be left unchanged.
Errors are stored as the conversion status in the
rstatus
argument.
EXAMPLES
The following example will always return a number in
[1..99]
range no matter what the input is, and warn if
the conversion failed.
int e;
uintmax_t lval = strtou(buf, NULL, 0, 1, 99, &e);
if (e)
warnc(e, "conversion of `%s' to a number failed, using %ju",
buf, lval);
ERRORS
-
-
- [
ECANCELED
]
- The string did not contain any characters that were
converted.
-
-
- [
EINVAL
]
- The base is not between 2 and 36 and
does not contain the special value 0.
-
-
- [
ENOTSUP
]
- The string contained non-numeric characters that did not
get converted. In this case, endptr points to the
first unconverted character.
-
-
- [
ERANGE
]
- The given string was out of range; the value converted has
been clamped; or the range given was invalid, i.e.
lo > hi.
SEE ALSO
atof(3),
atoi(3),
atol(3),
atoll(3),
strtod(3),
strtoi(3),
strtoimax(3),
strtol(3),
strtoll(3),
strtoul(3),
strtoull(3),
strtoumax(3)
STANDARDS
The
strtou() function is a
NetBSD
extension.
HISTORY
The
strtou() function first appeared in
NetBSD 7.
OpenBSD introduced
the
strtonum(
3) function for the same
purpose, but the interface makes it impossible to properly differentiate
illegal returns.
BUGS
Ignores the current locale.