strtoul(3) - NetBSD Manual Pages

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STRTOUL(3)              NetBSD Library Functions Manual             STRTOUL(3)


NAME

     strtoul, strtoull, strtoumax, strtouq -- convert a string to an unsigned
     long, unsigned long long, uintmax_t or uquad_t integer


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #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>

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

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

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


DESCRIPTION

     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' 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 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.)


RETURN VALUES

     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, 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 no error occurs, errno is left unchanged.  This behavior (which is
     unlike most library functions) is guaranteed by the pertinent standards.


EXAMPLES

     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
     afterwards:

           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).


ERRORS

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


SEE ALSO

     strtoimax(3), strtol(3), strtoll(3)


STANDARDS

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


BUGS

     Ignores the current locale.

NetBSD 5.2                       July 23, 2009                      NetBSD 5.2