strtoul(3) — Linux manual page


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

NAME         top

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

SYNOPSIS         top

       #include <stdlib.h>

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

   Feature Test Macro Requirements for glibc (see

               || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION         top

       The strtoul() function converts the initial part of the string in
       nptr to an unsigned long 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 unsigned long
       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, 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 value.

RETURN VALUE         top

       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).

ERRORS         top

       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).

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                      Attribute     Value          │
       │strtoul(), strtoull(),         │ Thread safety │ MT-Safe locale │
       │strtouq()                      │               │                │

CONFORMING TO         top

       strtoul(): POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4.

       strtoull(): POSIX.1-2001, POSIX.1-2008, C99.

NOTES         top

       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.

       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_t strtouq(const char *nptr, char **endptr, int base);

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

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

EXAMPLES         top

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at

GNU                            2021-03-22                     STRTOUL(3)

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