STRTOUL(3)

NAME
strtoul, strtoul_l, strtoull, strtoull_l, strtoumax, strtoumax_l, strtouq, strtouq_l - 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);
#include <xlocale.h>
unsigned long
strtoul_l(const char *nptr, char **endptr, int base, locale_t loc);
unsigned long long
strtoull_l(const char *nptr, char **endptr, int base, locale_t loc);
uintmax_t
strtoumax_l(const char *nptr, char **endptr, int base, locale_t loc);
u_quad_t
strtouq_l(const char *nptr, char **endptr, int base, locale_t loc);

DESCRIPTION
The strtoul() and strtoul_l() functions convert the string in nptr to an unsigned long value. The strtoull() and strtoull_l() functions convert the string in nptr to an unsigned long long value. The strtoumax() and strtoumax_l() functions convert the string in nptr to a umaxint_t value. The strtouq() and strtouq_l() functions are deprecated equivalents of strtoull() and strtoull_l() and are 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, unsigned long long, or uintmax_t 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.)

The functions with postfix "_l" use the locale provided as parameter, while the other functions use the current locale.

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(), strtoul_l(), strtoull(), strtoull_l(), strtoumax(), strtoumax_l(), strtoumax_l(), strtouq() and strtouq_l() 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() and strtoul_l() return ULONG_MAX, strtoull() and strtoull_l() return ULLONG_MAX, strtoumax() and strtoumax_l() returns UINTMAX_MAX, strtouq() and strtouq_l() returns ULLONG_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 there is no valid digit, 0 is returned. If base is invalid, 0 is returned and the global variable errno is set to EINVAL.

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

[EINVAL]
    The value of base was neither between 2 and 36 inclusive nor the special value 0.

[ERANGE]
    The given string was out of range; the value converted has been clamped.

SEE ALSO
sscanf(3), strtol(3) xlocale(3)

STANDARDS
The strtoul(), strtoull(), and strtoumax() functions conform to isoC-99. Setting errno to EINVAL is an extension to that standard required by p1003.1-2008.

The strtouq() function is a BSD extension and is provided for backwards compatibility with legacy programs. The strtoul_l(), strtoull_l(), strtoumax_l() and strtouq_l() functions are Darwin extensions.

BUGS