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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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STRTOUL(3P) POSIX Programmer's Manual STRTOUL(3P)
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.
strtoul, strtoull — convert a string to an unsigned long
#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);
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.
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].
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.
None.
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.
None.
None.
fscanf(3p), isalpha(3p), strtod(3p), strtol(3p)
The Base Definitions volume of POSIX.1‐2017, stdlib.h(0p)
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 .
IEEE/The Open Group 2017 STRTOUL(3P)
Pages that refer to this page: stdlib.h(0p), a64l(3p), fscanf(3p), strtoimax(3p)
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HTML rendering created 2025-09-06 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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