strtoul, strtoull, strtouq - convert a string to an unsigned
long or unsigned
long long integer
#include <stdlib.h>
#include <limits.h>
unsigned long
strtoul(const char *nptr, char **endptr, int base);
#include <stdlib.h>
#include <limits.h>
unsigned long long
strtoull(const char *nptr, char **endptr, int base);
#include <sys/types.h>
#include <stdlib.h>
#include <limits.h>
u_quad_t
strtouq(const char *nptr, char **endptr, int base);
The strtoul() function converts the string in nptr to an unsigned long
value. The strtoull() function converts the string in nptr
to an
unsigned long long value. The strtouq() function is a deprecated equivalent
of strtoull() and is provided for backwards compatibility with legacy
programs. The conversion is done according to the given
base, which
must be a number between 2 and 36 inclusive or the special
value 0. If
the string in nptr represents a negative number, it will be
converted to
its unsigned equivalent. This behavior is consistent with
what happens
when a signed integer type is cast to its unsigned counterpart.
The string may begin with an arbitrary amount of whitespace
(as determined
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 end of the string or at the
first character
that does not produce a valid digit in the given base.
(In bases
above 10, the letter `A' in either upper or lower case represents 10, `B'
represents 11, and so forth, with `Z' representing 35.)
If endptr is non-null, strtoul() stores the address of the
first invalid
character in *endptr. If there were no digits at all, however, strtoul()
stores the original value of nptr in *endptr. (Thus, if
*nptr is not
` ' but **endptr is ` ' on return, the entire string was
valid.)
The strtoul() function returns the result of the conversion,
unless the
value would overflow, in which case ULONG_MAX is returned
and errno is
set to ERANGE. If there was a leading minus sign, strtoul()
returns the
(unsigned) negation of the absolute value of the number, unless the absolute
value would overflow. In this case, strtoul() returns
ULONG_MAX and
sets the global variable errno to ERANGE.
The strtoull() function has identical return values except
that
ULLONG_MAX is used to indicate overflow.
There is no way to determine if strtoul() has processed a
negative number
(and returned an unsigned value) short of examining the
string in nptr
directly.
Ensuring that a string is a valid number (i.e., in range and
containing
no trailing characters) requires clearing errno beforehand
explicitly
since errno is not changed on a successful call to
strtoul(), and the return
value of strtoul() cannot be used unambiguously to signal an error:
char *ep;
unsigned long ulval;
...
errno = 0;
ulval = strtoul(buf, &ep, 10);
if (buf[0] == ' ' || *ep != ' ')
goto not_a_number;
if (errno == ERANGE && ulval == ULONG_MAX)
goto out_of_range;
This example will accept ``12'' but not ``12foo'' or ``120'.
If trailing
whitespace is acceptable, further checks must be done on
*ep; alternately,
use sscanf(3).
[ERANGE] The given string was out of range; the value
converted has
been clamped.
sscanf(3), strtol(3)
The strtoul() and strtoull() functions conform to ANSI/ISO/IEC 9899-1999
(``ANSI C99''). The strtouq() function is a BSD extension
and is provided
for backwards compatibility with legacy programs.
Ignores the current locale.
OpenBSD 3.6 June 25, 1992
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