STRTOUL(3)

NAME
strtoul, strtoull, strtouq - convert a string to an unsigned long integer

SYNOPSIS
#include <stdlib.h>

unsigned long int
strtoul(const char *nptr, char **endptr, int base);

unsigned long long int
strtoull(const char *nptr, char **endptr, int base);

DESCRIPTION
The strtoul() function converts the initial part of the string in nptr to an unsigned long integer value according to the given base, which must be between 2 and 36 inclusive, or be the special value 0.

The string must 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 8 (octal).

The remainder of the string is converted to an unsigned long int value in the obvious manner, stopping at the first character which is not 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 not NULL, strtoul() stores the address of the first invalid character in *endptr. If there were no digits at all, strtoul() stores the original value of nptr in *endptr (and returns 0). In particular, if *nptr is not `\0' but **endptr is `\0' on return, the entire string is valid.

The strtoull() function works just like the strtoul() function but returns an unsigned long long integer value.

RETURN VALUE
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 and sets the global variable errno to ERANGE. Precisely the same holds for strtoull() (with ULLONG_MAX instead of ULONG_MAX).

ERRORS

EINVAL
    (not in C99) The given base contains an unsupported value.

ERANGE
    The resulting value was out of range.

The implementation may also set errno to EINVAL in case no conversion was performed (no digits seen, and 0 returned).

NOTES
In locales other than the "C" locale, also other strings may be accepted. (For example, the thousands separator of the current locale may be supported.)

BSD also has

u_quad_t
strtouq(const char *nptr, char **endptr, int base);

with completely analogous definition. Depending on the wordsize of the current architecture, this may be equivalent to strtoull() or to strtoul().

CONFORMING TO
strtoul() conforms to SVID 3, 4.3BSD, ISO 9899 (C99) and POSIX, and strtoull() to ISO 9899 (C99) and POSIX 1003.1-2001.

SEE ALSO
atof(3), atoi(3), atol(3), strtod(3), strtol(3)