Tribblix: manual page: strtoul.3c

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