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'\" t
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" References consulted:
.\" Linux libc source code
.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\" 386BSD man pages
.\" Modified Sun Jul 25 10:54:03 1993 by Rik Faith (faith@cs.unc.edu)
.\" Fixed typo, aeb, 950823
.\" 2002-02-22, joey, mihtjel: Added strtoull()
.\"
.TH strtoul 3 2024-05-02 "Linux man-pages (unreleased)"
.SH NAME
strtoul, strtoull, strtouq \- convert a string to an unsigned long integer
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.P
.BI "unsigned long strtoul(const char *restrict " nptr ,
.BI " char **restrict " endptr ", int " base );
.BI "unsigned long long strtoull(const char *restrict " nptr ,
.BI " char **restrict " endptr ", int " base );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR strtoull ():
.nf
_ISOC99_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
.fi
.SH DESCRIPTION
The
.BR strtoul ()
function converts the initial part of the string
in
.I nptr
to an
.I "unsigned long"
value according to the
given
.IR base ,
which must be between 2 and 36 inclusive, or be
the special value 0.
.P
The string may begin with an arbitrary amount of white space (as
determined by
.BR isspace (3))
followed by a single optional \[aq]+\[aq] or \[aq]\-\[aq]
sign.
If
.I 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
.I base
is taken as 10 (decimal) unless the next character
is \[aq]0\[aq], in which case it is taken as 8 (octal).
.P
The remainder of the string is converted to an
.I "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 \[aq]A\[aq] in
either uppercase or lowercase represents 10, \[aq]B\[aq] represents 11, and so
forth, with \[aq]Z\[aq] representing 35.)
.P
If
.I endptr
is not NULL,
and the
.I base
is supported,
.BR strtoul ()
stores the address of the
first invalid character in
.IR *endptr .
If there were no digits at
all,
.BR strtoul ()
stores the original value of
.I nptr
in
.I *endptr
(and returns 0).
In particular, if
.I *nptr
is not \[aq]\e0\[aq] but
.I **endptr
is \[aq]\e0\[aq] on return, the entire string is valid.
.P
The
.BR strtoull ()
function works just like the
.BR strtoul ()
function but returns an
.I "unsigned long long"
value.
.SH RETURN VALUE
The
.BR 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,
.BR strtoul ()
returns
.B ULONG_MAX
and sets
.I errno
to
.BR ERANGE .
Precisely the same holds for
.BR strtoull ()
(with
.B ULLONG_MAX
instead of
.BR ULONG_MAX ).
.SH ERRORS
This function does not modify
.I errno
on success.
.TP
.B EINVAL
(not in C99)
The given
.I base
contains an unsupported value.
.TP
.B ERANGE
The resulting value was out of range.
.P
The implementation may also set
.I errno
to
.B EINVAL
in case
no conversion was performed (no digits seen, and 0 returned).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR strtoul (),
.BR strtoull (),
.BR strtouq ()
T} Thread safety MT-Safe locale
.TE
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
.TP
.BR strtoul ()
POSIX.1-2001, C89, SVr4.
.TP
.BR strtoull ()
POSIX.1-2001, C99.
.SH NOTES
Since
.BR strtoul ()
can legitimately return 0 or
.B ULONG_MAX
.RB ( ULLONG_MAX
for
.BR strtoull ())
on both success and failure, the calling program should set
.I errno
to 0 before the call,
and then determine if an error occurred by checking whether
.I errno
has a nonzero value after the call.
.P
In locales other than the "C" locale, other strings may be accepted.
(For example, the thousands separator of the current locale may be
supported.)
.P
BSD also has
.P
.in +4n
.EX
.BI "u_quad_t strtouq(const char *" nptr ", char **" endptr ", int " base );
.EE
.in
.P
with completely analogous definition.
Depending on the wordsize of the current architecture, this
may be equivalent to
.BR strtoull ()
or to
.BR strtoul ().
.P
Negative values are considered valid input and are
silently converted to the equivalent
.I "unsigned long"
value.
.SH EXAMPLES
See the example on the
.BR strtol (3)
manual page;
the use of the functions described in this manual page is similar.
.SH SEE ALSO
.BR a64l (3),
.BR atof (3),
.BR atoi (3),
.BR atol (3),
.BR strtod (3),
.BR strtol (3),
.BR strtoumax (3)
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