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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | CAVEATS | EXAMPLES | SEE ALSO | COLOPHON |
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strtoul(3) Library Functions Manual strtoul(3)
strtoul, strtoull, strtouq - convert a string to an unsigned long
integer
Standard C library (libc, -lc)
#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
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.
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).
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).
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────┼───────────────┼────────────────┤
│ strtoul(), strtoull(), │ Thread safety │ MT-Safe locale │
│ strtouq() │ │ │
└──────────────────────────────┴───────────────┴────────────────┘
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().
C11, POSIX.1-2008.
strtoul()
POSIX.1-2001, C89, SVr4.
strtoull()
POSIX.1-2001, C99.
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.
See the example on the strtol(3) manual page; the use of the
functions described in this manual page is similar.
a64l(3), atof(3), atoi(3), atol(3), strtod(3), strtol(3),
strtoumax(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨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⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.9.1 2024-06-16 strtoul(3)
Pages that refer to this page: capsh(1), a64l(3), atof(3), atoi(3), sscanf(3), strtod(3), strtoimax(3), strtol(3), bpf-helpers(7), logrotate(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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