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

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

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

           _ISOC99_SOURCE ||
               || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION         top

       The strtoul() function converts the initial part of the string in
       nptr to an unsigned long int 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 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 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 int 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(), strtouq() │ Thread safety │ MT-Safe locale │

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

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

       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

       Negative values are considered valid input and are silently converted
       to the equivalent unsigned long int 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 5.08 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                              2020-06-09                       STRTOUL(3)

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