strtoul, strtoull, strtouq - convert a string to an unsigned long integer
#include <stdlib.h>
unsigned long strtoul(const char *restrict nptr,
char **restrict endptr, int base);
unsigned long long strtoull(const char *restrict nptr,
char **restrict endptr, int base);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
The strtoul() function converts the initial part of
the string in nptr
to an unsigned long
value 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" 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 unsigned long
value in the obvious manner, stopping at the first character which is
not a valid digit in the given base. (In bases above 10, the letter 'A'
in either uppercase or lowercase represents 10, 'B' represents 11, and
so forth, with 'Z' representing 35.)
If endptr
is not NULL, and the base
is supported,
strtoul() stores the address of the first invalid
character in *endptr
. If there were no digits at all,
strtoul() stores the original value of nptr
in
*endptr
(and returns 0). In particular, if *nptr
is
not '\0' but **endptr
is '\0' on return, the entire string is
valid.
The strtoull() function works just like the strtoul() function but returns an unsigned long long value.
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 represented as an unsigned value, unless
the original (nonnegated) value would overflow; in the latter case,
strtoul() returns ULONG_MAX and sets
errno
to ERANGE. Precisely the same holds for
strtoull() (with ULLONG_MAX instead of
ULONG_MAX).
See the example on the strtol(3) manual page; the use of the functions described in this manual page is similar.