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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
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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.1‐2017 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 representation, 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 followed by a sequence of the digits '0' to '7' only. A hexadecimal constant
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 subject sequence is a sequence of
letters and digits representing an integer 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 <hyphen-minus>,
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, provided that endptr is not a null pointer.
In other than the C or POSIX locale, additional locale-specific subject sequence forms 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
strtoull(), 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 ALSO
fscanf(), isalpha(), strtod(), strtol()
The Base Definitions volume of POSIX.1‐2017, <stdlib.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/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.kernel.org/doc/man-pages/reporting_bugs.html .