strtoul() - convert a string to an unsigned long
#include <stdlib.h>
#include <limits.h>
unsigned long strtoul (const char *nptr, char **endptr, int base)
The strtoul(3) function converts the string in nptr to an unsigned long 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 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 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 not nil, strtoul(3) stores the address
of the first invalid character in *endptr. If there were no
digits at all, however, strtoul(3) stores the original value of
nptr in *endptr. (Thus, if *nptr is not
\0 but **endptr is \0 on return,
the entire string was valid.)
The strtoul(3) 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(3) returns {ULONG_MAX} and sets the global variable errno to [ERANGE].
strtol(3)