STRTOUL(3) BSD Programmer's Manual STRTOUL(3)
strtoul, strtoull, strtouq - convert a string to an unsigned long or un-
signed 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 <inttypes.h>
uintmax_t
strtoumax(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 pro-
grams. 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 un-
signed 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 deter-
mined 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 charac-
ter 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.)
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 abso-
lute 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 re-
turn 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 whi-
tespace 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(), strtoull() and strtoumax() functions conform to ISO/IEC
9899:1999 ("ISO C99"). The strtouq() function is a BSD extension and is
provided for backwards compatibility with legacy programs.
Ignores the current locale.
MirBSD #10-current March 19, 2014 1