strtoul(3) Library Functions Manual strtoul(3)
NAME
strtoul, strtoull, strtouq - convert a string to an unsigned long inte-
ger
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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
DESCRIPTION
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 be-
tween 2 and 36 inclusive, or be the special value 0.
The string may begin with an arbitrary amount of white space (as deter-
mined 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 re-
turns an unsigned long long value.
RETURN 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 (non-
negated) value would overflow; in the latter case, strtoul() returns
ULONG_MAX and sets errno to ERANGE. Precisely the same holds for str-
toull() (with ULLONG_MAX instead of ULONG_MAX).
ERRORS
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).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌─────────────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼────────────────┤
│ strtoul(), strtoull(), strtouq() │ Thread safety │ MT-Safe locale │
└─────────────────────────────────────┴───────────────┴────────────────┘
VERSIONS
In locales other than the "C" locale, other strings may be accepted.
(For example, the thousands separator of the current locale may be sup-
ported.)
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 str-
toul().
STANDARDS
C11, POSIX.1-2008.
HISTORY
strtoul()
POSIX.1-2001, C89, SVr4.
strtoull()
POSIX.1-2001, C99.
CAVEATS
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.
EXAMPLES
See the example on the strtol(3) manual page; the use of the functions
described in this manual page is similar.
SEE ALSO
a64l(3), atof(3), atoi(3), atol(3), strtod(3), strtol(3), strtoumax(3)
Linux man-pages 6.9.1 2024-06-16 strtoul(3)
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