STRTOUL(3) OpenBSD Programmer's Manual STRTOUL(3)NAME
strtoul, strtoull, strtoumax, strtouq - convert a string to an unsigned
long, unsigned long long or uintmax_t integer
SYNOPSIS
#include <limits.h>
#include <stdlib.h>
unsigned long
strtoul(const char *nptr, char **endptr, int base);
unsigned long long
strtoull(const char *nptr, char **endptr, int base);
#include <inttypes.h>
uintmax_t
strtoumax(const char *nptr, char **endptr, int base);
#include <sys/types.h>
#include <limits.h>
#include <stdlib.h>
u_quad_t
strtouq(const char *nptr, char **endptr, int base);
DESCRIPTION
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 strtoumax() function converts the string
in nptr to a umaxint_t 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
`\0' but **endptr is `\0' on return, the entire string was valid.)
RETURN VALUES
The strtoul(), strtoull(), strtoumax() and strtouq() functions return
either the result of the conversion or, if there was a leading minus
sign, the negation of the result of the conversion, unless the original
(non-negated) value would overflow. If overflow occurs, strtoul()
returns ULONG_MAX, strtoull() returns ULLONG_MAX, strtoumax() returns
UINTMAX_MAX, strtouq() returns ULLONG_MAX and the global variable errno
is set to ERANGE. If no conversion could be performed, 0 is returned;
the global variable errno is also set to EINVAL, though this is not
portable across all platforms.
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.
EXAMPLES
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] == '\0' || *ep != '\0')
goto not_a_number;
if (errno == ERANGE && ulval == ULONG_MAX)
goto out_of_range;
This example will accept ``12'' but not ``12foo'' or ``12\n''. If
trailing whitespace is acceptable, further checks must be done on *ep;
alternately, use sscanf(3).
ERRORS
[ERANGE] The given string was out of range; the value converted has
been clamped.
SEE ALSOsscanf(3), strtol(3)STANDARDS
The strtoul(), strtoull(), and strtoumax() 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.
BUGS
Ignores the current locale.
OpenBSD 4.9 April 7, 2010 OpenBSD 4.9
