STRTOUL(3) Library Functions Manual STRTOUL(3)
strtoul, strtoull, strtoumax, strtouq -- convert a string to an unsigned
long, unsigned long long, uintmax_t or uquad_t integer
Standard C Library (libc, -lc)
unsigned long int
strtoul(const char * restrict nptr, char ** restrict endptr, int base);
unsigned long long int
strtoull(const char * restrict nptr, char ** restrict endptr, int base);
strtoumax(const char * restrict nptr, char ** restrict endptr, int base);
strtouq(const char * restrict nptr, char ** restrict endptr, int base);
The strtoul() function converts the string in nptr to an unsigned long
int value. The strtoull() function converts the string in nptr to an
unsigned long long int value. The strtoumax() function converts the
string in nptr to an uintmax_t value. The strtouq() function converts
the string in nptr to a u_quad_t value. The conversion is done according
to the given base, which must be between 2 and 36 inclusive, or be the
special value 0.
The string may begin with an arbitrary amount of white space (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
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-nil, 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 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; in
the latter case, strtoul() returns ULONG_MAX, strtoull() returns
ULLONG_MAX, strtoumax() returns UINTMAX_MAX, strtouq() returns UQUAD_MAX,
and the global variable errno is set to ERANGE.
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. If the base argument is not supported then errno is set to
EINVAL and the functions return 0.
If no error occurs, errno is left unchanged. This behavior (which is
unlike most library functions) is guaranteed by the pertinent standards.
Because the return value of strtoul() cannot be used unambiguously to
detect an error, errno is left unchanged after a successful call. To
ensure that a string is a valid number (i.e., in range and containing no
trailing characters), clear errno beforehand explicitly, then check it
unsigned long ulval;
errno = 0;
ulval = strtoul(buf, &ep, 10);
if (buf == '\0' || *ep != '\0')
if (errno == ERANGE && ulval == ULONG_MAX)
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).
[EINVAL] The base is not between 2 and 36 and does not contain
the special value 0.
[ERANGE] The given string was out of range; the value converted
has been clamped.
strtoimax(3), strtol(3), strtoll(3)
The strtoul() function conforms to ANSI X3.159-1989 (``ANSI C89''). The
strtoull() and strtoumax() functions conform to ISO/IEC 9899:1999
Ignores the current locale.
NetBSD 6.1.5 December 2, 2009 NetBSD 6.1.5