strtoul---string to unsigned long
#include <stdlib.h>
unsigned long strtoul(const char *s, char **ptr,
int base);
unsigned long _strtoul_r(void *reent, const char *s,
char **ptr, int base);
Description
The function strtoul converts the string *s to
an unsigned long. First, it breaks down the string into three parts:
leading whitespace, which is ignored; a subject string consisting
of the digits meaningful in the radix specified by base
(for example, 0 through 7 if the value of base is 8);
and a trailing portion consisting of one or more unparseable characters,
which always includes the terminating null character. Then, it attempts
to convert the subject string into an unsigned long integer, and returns the
result.
If the value of base is zero, the subject string is expected to look
like a normal C integer constant (save that no optional sign is permitted):
a possible 0x indicating hexadecimal radix, and a number.
If base is between 2 and 36, the expected form of the subject is a
sequence of digits (which may include letters, depending on the
base) representing an integer in the radix specified by base.
The letters a--z (or A--Z) are used as digits valued from
10 to 35. If base is 16, a leading 0x is permitted.
The subject sequence is the longest initial sequence of the input string that has the expected form, starting with the first non-whitespace character. If the string is empty or consists entirely of whitespace, or if the first non-whitespace character is not a permissible digit, the subject string is empty.
If the subject string is acceptable, and the value of base is zero,
strtoul attempts to determine the radix from the input string. A
string with a leading 0x is treated as a hexadecimal value; a string with
a leading 0 and no x is treated as octal; all other strings are
treated as decimal. If base is between 2 and 36, it is used as the
conversion radix, as described above. Finally, a pointer to the first
character past the converted subject string is stored in ptr, if
ptr is not NULL.
If the subject string is empty (that is, if *s does not start
with a substring in acceptable form), no conversion
is performed and the value of s is stored in ptr (if ptr is
not NULL).
The alternate function _strtoul_r is a reentrant version. The
extra argument reent is a pointer to a reentrancy structure.
Returns
strtoul returns the converted value, if any. If no conversion was
made, 0 is returned.
strtoul returns ULONG_MAX if the magnitude of the converted
value is too large, and sets errno to ERANGE.
Portability
strtoul is ANSI.
strtoul requires no supporting OS subroutines.
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