strtoul(3) — Linux manual page

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | CAVEATS | EXAMPLES | SEE ALSO | COLOPHON

strtoul(3)               Library Functions Manual              strtoul(3)

NAME         top

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

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <stdlib.h>

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

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

       strtoull():
           _ISOC99_SOURCE
               || /* 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, 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 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

       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).

ATTRIBUTES         top

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

VERSIONS         top

       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().

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

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

       strtoull()
              POSIX.1-2001, C99.

CAVEATS         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.

       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),
       strtoumax(3)

COLOPHON         top

       This page is part of the man-pages (Linux kernel and C library
       user-space interface documentation) project.  Information about
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       ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
       for this manual page, see
       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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       man-pages@man7.org

Linux man-pages 6.10            2024-07-23                     strtoul(3)

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