STRTOUL(3P) POSIX Programmer's Manual STRTOUL(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
strtoul, strtoull — convert a string to an unsigned long
SYNOPSIS
#include <stdlib.h>
unsigned long strtoul(const char *restrict str,
char **restrict endptr, int base);
unsigned long long strtoull(const char *restrict str,
char **restrict endptr, int base);
DESCRIPTION
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here
and the ISO C standard is unintentional. This volume of POSIX.1‐2008
defers to the ISO C standard.
These functions shall convert the initial portion of the string pointed
to by str to a type unsigned long and unsigned long long representa‐
tion, respectively. First, they decompose the input string into three
parts:
1. An initial, possibly empty, sequence of white-space characters (as
specified by isspace())
2. A subject sequence interpreted as an integer represented in some
radix determined by the value of base
3. A final string of one or more unrecognized characters, including
the terminating NUL character of the input string
Then they shall attempt to convert the subject sequence to an unsigned
integer, and return the result.
If the value of base is 0, the expected form of the subject sequence is
that of a decimal constant, octal constant, or hexadecimal constant,
any of which may be preceded by a '+' or '−' sign. A decimal constant
begins with a non-zero digit, and consists of a sequence of decimal
digits. An octal constant consists of the prefix '0' optionally fol‐
lowed by a sequence of the digits '0' to '7' only. A hexadecimal con‐
stant consists of the prefix 0x or 0X followed by a sequence of the
decimal digits and letters 'a' (or 'A') to 'f' (or 'F') with values 10
to 15 respectively.
If the value of base is between 2 and 36, the expected form of the sub‐
ject sequence is a sequence of letters and digits representing an inte‐
ger with the radix specified by base, optionally preceded by a '+' or
'−' sign. The letters from 'a' (or 'A') to 'z' (or 'Z') inclusive are
ascribed the values 10 to 35; only letters whose ascribed values are
less than that of base are permitted. If the value of base is 16, the
characters 0x or 0X may optionally precede the sequence of letters and
digits, following the sign if present.
The subject sequence is defined as the longest initial subsequence of
the input string, starting with the first non-white-space character
that is of the expected form. The subject sequence shall contain no
characters if the input string is empty or consists entirely of white-
space characters, or if the first non-white-space character is other
than a sign or a permissible letter or digit.
If the subject sequence has the expected form and the value of base is
0, the sequence of characters starting with the first digit shall be
interpreted as an integer constant. If the subject sequence has the
expected form and the value of base is between 2 and 36, it shall be
used as the base for conversion, ascribing to each letter its value as
given above. If the subject sequence begins with a minus-sign, the
value resulting from the conversion shall be negated. A pointer to the
final string shall be stored in the object pointed to by endptr, pro‐
vided that endptr is not a null pointer.
In other than the C or POSIX locales, other implementation-defined sub‐
ject sequences may be accepted.
If the subject sequence is empty or does not have the expected form, no
conversion shall be performed; the value of str shall be stored in the
object pointed to by endptr, provided that endptr is not a null
pointer.
These functions shall not change the setting of errno if successful.
Since 0, {ULONG_MAX}, and {ULLONG_MAX} are returned on error and are
also valid returns on success, an application wishing to check for
error situations should set errno to 0, then call strtoul() or str‐
toull(), then check errno.
RETURN VALUE
Upon successful completion, these functions shall return the converted
value, if any. If no conversion could be performed, 0 shall be returned
and errno may be set to [EINVAL].
If the value of base is not supported, 0 shall be returned and errno
shall be set to [EINVAL].
If the correct value is outside the range of representable values,
{ULONG_MAX} or {ULLONG_MAX} shall be returned and errno set to
[ERANGE].
ERRORS
These functions shall fail if:
EINVAL The value of base is not supported.
ERANGE The value to be returned is not representable.
These functions may fail if:
EINVAL No conversion could be performed.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Since the value of *endptr is unspecified if the value of base is not
supported, applications should either ensure that base has a supported
value (0 or between 2 and 36) before the call, or check for an [EINVAL]
error before examining *endptr.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOfscanf(), isalpha(), strtod(), strtol()
The Base Definitions volume of POSIX.1‐2008, <stdlib.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 STRTOUL(3P)
