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

       For an explanation of the terms used in this section, see attributes(7).
       ┌──────────────────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │ Interface                                                            │ Attribute     │ Value          │
       ├──────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │ strtoul(), strtoull(), strtouq()                                     │ Thread safety │ MT-Safe locale │
       └──────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┘

       Since  strtoul()  can  legitimately return 0 or ULONG_MAX (ULLONG_MAX for strtoull()) on both success and
       failure, the calling program should set errno to 0 before the  call,  and  then  determine  if  an  error
       occurred by checking whether errno has a nonzero value after the call.

       Negative  values  are  considered  valid input and are silently converted to the equivalent unsignedlong
       value.

       The  strtoul()  function  converts  the  initial  part  of  the  string in nptr to an unsignedlong value
       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 unsignedlong 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 uppercase or lowercase represents 10, 'B' represents 11, and so forth, with 'Z' representing 35.)

       If endptr is not NULL, and the base is supported, 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 unsignedlonglong value.

       This function does not modify errno on success.

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

       ERANGE The resulting value was out of range.

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

       See the example on the strtol(3) manual page; the use of the functions described in this manual  page  is
       similar.

strtoul()
              POSIX.1-2001, C89, SVr4.

       strtoull()
              POSIX.1-2001, C99.

       Standard C library (libc, -lc)

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

       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 represented as an unsigned value, unless the original
       (nonnegated) value would overflow; in the latter case, strtoul() returns  ULONG_MAX  and  sets  errno  to
       ERANGE.  Precisely the same holds for strtoull() (with ULLONG_MAX instead of ULONG_MAX).

a64l(3), atof(3), atoi(3), atol(3), strtod(3), strtol(3), strtoumax(3)

Linux man-pages 6.9.1                              2024-06-16                                         strtoul(3)

       C11, POSIX.1-2008.

#include<stdlib.h>unsignedlongstrtoul(constchar*restrictnptr,char**_Nullablerestrictendptr,intbase);unsignedlonglongstrtoull(constchar*restrictnptr,char**_Nullablerestrictendptr,intbase);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       strtoull():
           _ISOC99_SOURCE
               || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

       In locales other than the "C" locale, other  strings  may  be  accepted.   (For  example,  the  thousands
       separator of the current locale may be supported.)

       BSD also has

           u_quad_tstrtouq(constchar*nptr,char**endptr,intbase);

       with completely analogous definition.  Depending on the wordsize of the current architecture, this may be
       equivalent to strtoull() or to strtoul().