man strtoul (strtoull)

man strtoul
STRTOUL(3)                             Linux Programmer's Manual                            STRTOUL(3)

NAME
       strtoul, strtoull - convert a string to an unsigned long integer.

SYNOPSIS
       #include

       unsigned long int
       strtoul(const char *nptr, char **endptr, int base);

       unsigned long long int
       strtoull(const char *nptr, char **endptr, int base);

DESCRIPTION
       The  strtoul()  function  converts  the  initial part of the string in nptr to an unsigned long
       integer value according to the given base, which must be between 2 and 36 inclusive, or be  the
       special value 0.

       The  string  must  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 int 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 upper or lower case represents  10,  `B'  represents  11,  and  so
       forth, with `Z' representing 35.)

       If  endptr is not NULL, 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 integer value.

RETURN 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,  unless  the  original  (non-negated)
       value would overflow; in the latter case, strtoul() returns ULONG_MAX and sets the global vari-
       able errno to ERANGE.  Precisely the same holds for  strtoull()  (with  ULLONG_MAX  instead  of
       ULONG_MAX).

ERRORS
       ERANGE The resulting value was out of range.

       EINVAL (not in C99) The given base contains an unsupported value.

       The  implementation may also set errno to EINVAL in case no conversion was performed (no digits
       seen, and 0 returned).

NOTE
       In locales other than the "C" locale, also other strings may be accepted.

CONFORMING TO
       strtoul() conforms to SVID 3, BSD 4.3, ISO 9899 (C99) and POSIX, and  strtoull()  to  ISO  9899
       (C99) and POSIX-2001.

SEE ALSO
       atof(3), atoi(3), atol(3), strtod(3), strtol(3)

GNU                                           2002-02-22