The
strtoul() 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' 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 non-nil,
strtoul() stores the address of the first invalid character in
*endptr. If there were no digits at all, however,
strtoul() 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.)