strtoul, strtoull - convert string to unsigned long
unsigned long strtoul(const char *str, char **endptr, int
unsigned long long strtoull(const char *str, char **endptr,
The strtoul() function converts the initial portion of the
string pointed to by str to a type unsigned long int
representation. First it decomposes the input string into
three parts: an initial, possibly empty, sequence of white-
space characters (as specified by isspace(3C)); a subject
sequence interpreted as an integer represented in some radix
determined by the value of base; and a final string of one
or more unrecognised characters, including the terminating
null byte of the input string. Then it attempts to convert
the subject sequence to an unsigned integer, and returns the
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
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 charac-
ters 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 contains 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 is interpreted as an integer constant. If the
subject sequence has the expected form and the value of base
is between 2 and 36, it is 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 result-
ing from the conversion is negated. A pointer to the final
string is stored in the object pointed to by endptr, pro-
vided that endptr is not a null pointer.
In other than the POSIX locale, additional implementation-
dependent subject sequence forms may be accepted.
If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of str
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
The strtoull() function is identical to strtoul() except
that it returns the value represented by str as an unsigned
Upon successful completion strtoul() returns the converted
value, if any. If no conversion could be performed, 0 is
returned and errno may be set to EINVAL. If the correct
value is outside the range of representable values,
ULONG_MAX is returned and errno is set to ERANGE.
The strtoul() function will fail if:
The value of base is not supported.
The value to be returned is not representable.
The strtoul() function may fail if:
No conversion could be performed.
Because 0 and ULONG_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(), then check errno and if it is non-zero, assume an
error has occurred.
Unlike strtod(3C) and strtol(3C), strtoul() must always
return a non-negative number; so, using the return value of
strtoul() for out-of-range numbers with strtoul() could
cause more severe problems than just loss of precision if
those numbers can ever be negative.
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | MT-Safe |
isalpha(3C), isspace(3C), scanf(3C), strtod(3C), strtol(3C),
Man(1) output converted with