STRTOUL(3) | Library Functions Manual | STRTOUL(3) |
strtoul
, strtoull
,
strtoumax
, strtouq
—
#include <stdlib.h>
#include <limits.h>
unsigned long int
strtoul
(const
char * restrict nptr,
char ** restrict endptr,
int base);
unsigned long long int
strtoull
(const
char * restrict nptr,
char ** restrict endptr,
int base);
#include <inttypes.h>
uintmax_t
strtoumax
(const
char * restrict nptr,
char ** restrict endptr,
int base);
#include <sys/types.h>
#include <stdlib.h>
#include <limits.h>
u_quad_t
strtouq
(const
char * restrict nptr,
char ** restrict endptr,
int base);
strtoul
() function converts the string in
nptr to an unsigned long int
value. The strtoull
() function converts the string in
nptr to an unsigned long long int
value. The strtoumax
() function converts the string in
nptr to an uintmax_t value. The
strtouq
() function converts the string in
nptr to a u_quad_t value.
The conversion is done according to the given base, which must be between 2 and 36 inclusive, or be the special value 0.
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 appropriate 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, the functions store
the address of the first invalid character in *endptr.
If there were no digits at all, however, the functions store the original
value of nptr in *endptr. (Thus,
if *nptr is not
‘\0
’ but
**endptr is ‘\0
’
on return, the entire string was valid.)
strtoul
() function returns either the result of the
conversion or, if there was a leading minus sign, the negation of the result
of the conversion, unless the original (non-negated) value would overflow; in
the latter case, strtoul
() returns
ULONG_MAX
, strtoull
() returns
ULLONG_MAX
, strtoumax
()
returns UINTMAX_MAX
, strtouq
()
returns UQUAD_MAX
, and the global variable
errno is set to ERANGE
.
There is no way to determine if strtoul
()
has processed a negative number (and returned an unsigned value) short of
examining the string in nptr directly. If the
base argument is not supported then
errno is set to EINVAL
and the
functions return 0.
If no error occurs, errno is left unchanged. This behavior (which is unlike most library functions) is guaranteed by the pertinent standards.
strtoul
() cannot be used
unambiguously to detect an error, errno is left
unchanged after a successful call. To ensure that a string is a valid number
(i.e., in range and containing no trailing characters), clear
errno beforehand explicitly, then check it afterwards:
char *ep; unsigned long ulval; ... errno = 0; ulval = strtoul(buf, &ep, 10); if (ep == buf) goto not_a_number; if (*ep != '\0') goto trailing_garbage; if (errno) { assert(errno == ERANGE); assert(ulval == ULONG_MAX); goto out_of_range; }
This example will accept “12” but not “12foo” or “12\n”. If trailing whitespace is acceptable, further checks must be done on *ep; alternately, use sscanf(3).
strtoul
() function conforms to ANSI
X3.159-1989 (“ANSI C89”). The
strtoull
() and strtoumax
()
functions conform to ISO/IEC 9899:1999
(“ISO C99”).
The strtouq
() function is a
BSD legacy function equivalent to
strtoull
() and should not be used in a new code.
November 13, 2015 | NetBSD 9.0 |