STRTOUL(3)              NetBSD 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)

     #include <stdlib.h>
     #include <limits.h>

     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);

     #include <inttypes.h>

     strtoumax(const char * restrict nptr, char ** restrict endptr, int base);

     #include <sys/types.h>
     #include <stdlib.h>
     #include <limits.h>

     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 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' or `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 appropriate 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-nil, the functions store the address of the first
     invalid character in *endptr.  If there were no digits at all, however,
     the functions store the original value of nptr in *endptr.  (Thus, if
     *nptr is not `\0' but **endptr is `\0' on return, the entire string was

     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 conver-
     sion, unless the original (non-negated) value would overflow; in the lat-
     ter 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

           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 trail-
     ing whitespace is acceptable, further checks must be done on *ep; alter-
     nately, 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.

     atof(3), atoi(3), atol(3), atoll(3), strtod(3), strtoi(3), strtoimax(3),
     strtol(3), strtoll(3), strtou(3)

     The strtoul() function conforms to ANSI X3.159-1989 (``ANSI C89'').  The
     strtoull() and strtoumax() functions conform to ISO/IEC 9899:1999
     (``ISO C99'').

     The strtouq() function is a BSD legacy function equivalent to strtoull()
     and should not be used in a new code.

     Ignores the current locale.

NetBSD 7.0                     November 13, 2015                    NetBSD 7.0

You can also request any man page by name and (optionally) by section:


Use the DEFAULT collection to view manual pages for third-party software.

©1994 Man-cgi 1.15, Panagiotis Christias <>
©1996-2015 Modified for NetBSD by Kimmo Suominen