Converts a number-representing string to an unsigned long type integer.
unsigned long strtoul (const char *nptr, char **endptr, long base);
nptr Pointer to a number-representing string to be converted
endptr Pointer to the storage area containing a pointer to the first character that does not represent an integer
base Radix of conversion (0 or 2 to 36)
Normal: If the string pointed by nptr begins with a character that does not represent an integer: 0
If the string pointed by nptr begins with a character that represents an integer: Converted data as an unsigned long type integer
Abnormal: If the converted data overflows: ULONG_MAX
If the converted result overflows, errno is set.
The strtoul function converts data, from the first digit up to the character before the first character that does not represent an integer, into an unsigned long type integer.
In the storage area pointed by endptr, the function sets up a pointer to the first character that does not represent an integer. If some characters that do not represent an integer come before the first digit, the value of nptr is set in this area. If endptr is NULL, nothing is set in this area.
If the value of base is 0, the rules described in section 3.1.3 (4), Integers, are observed at conversion. If the value of base is 2 to 36, it indicates the radix of conversion, where a (or A) to z (or Z) in the string to be converted correspond to numbers 10 to 35. If a character that is not smaller than the base value is found in the string to be converted, conversion stops immediately. A 0 after a sign is ignored at conversion. Similarly, 0x (or 0X) is ignored when base is 16.