NAME
strtoul
, strtoull
,
strtoumax
, strtouq
—
convert a string to an unsigned long,
unsigned long long, uintmax_t or u_quad_t integer
LIBRARY
library “libc”
SYNOPSIS
#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);
DESCRIPTION
Thestrtoul
()
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.)
RETURN VALUES
The 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.
EXAMPLES
Because the return value of 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).
ERRORS
- [
EINVAL
] - The base is not between 2 and 36 and does not contain the special value 0.
- [
ERANGE
] - The given string was out of range; the value converted has been clamped.
SEE ALSO
atof(3), atoi(3), atol(3), atoll(3), strtod(3), strtoi(3), strtoimax(3), strtol(3), strtoll(3), strtou(3)
STANDARDS
The 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.
BUGS
Ignores the current locale.