STRTOUL(3C) Standard C Library Functions STRTOUL(3C)


NAME


strtoul, strtoull - convert string to 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 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 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 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 resulting from the
conversion is negated. A pointer to the final string is stored in the
object pointed to by endptr, provided 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 long long.

RETURN VALUES


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.

ERRORS


The strtoul() function will fail if:

EINVAL
The value of base is not supported.


ERANGE
The value to be returned is not representable.


The strtoul() function may fail if:

EINVAL
No conversion could be performed.


USAGE


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.

ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO


isalpha(3C), isspace(3C), scanf(3C), strtod(3C), strtol(3C),
attributes(5), standards(5)


November 1, 2003 STRTOUL(3C)