Updated: 2025/Nov/16

Please read Privacy Policy. It's for your privacy.

STRTOU(3)                  Library Functions Manual                  STRTOU(3)

NAME
     strtou, strtou_l - convert a string value to a unitmax_t integer

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <inttypes.h>

     uintmax_t
     strtou(const char * restrict nptr, char ** restrict endptr, int base,
         uintmax_t lo, uintmax_t hi, int *rstatus);

     #include <locale.h>

     uintmax_t
     strtou_l(const char * restrict nptr, char ** restrict endptr, int base,
         uintmax_t lo, uintmax_t hi, int *rstatus, locale_t loc);

DESCRIPTION
     The strtou() generates the uintmax_t result value equivalent to the
     numeric string in nptr.  The strtou() function internally uses
     strtoumax(3) and then ensures that the result is in the range [lo .. hi].
     In addition it places a conversion status indicator, 0 if fully
     successful, in the integer addressed by the rstatus argument, if that is
     not NULL, allowing the errno gymnastics that other similar functions
     require to be avoided.  The rstatus argument can be NULL if the
     conversion status is to be ignored.

     The operation of strtou() is unspecified if lo is greater than hi.

     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' or `0X' prefix,
     after which there must immediately follow at least one hexadecimal digit,
     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 the uintmax_t result in the
     obvious manner, stopping at the end of the string or 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, strtou() stores the address of the first character
     after those which were converted in *endptr.  If there were no digits at
     all, however, or if the base is invalid, strtou() 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.)  Note that converting an
     out of range value has no impact upon the value placed into *endptr.

     The strtou_l() function is identical, except uses the locale given by loc
     rather than the current locale, when determining what is white space to
     be skipped before the conversion begins.

RETURN VALUES
     The strtou() function, returns the converted value, or the closest value
     in the range specified by the lo and hi arguments, if the value converted
     was outside that range.  If lo is equal to hi and no overriding error
     occurs, that value will always be returned.

     The errno value from <errno.h>, is guaranteed to be left unchanged.

     Errors are stored as the conversion status error indicator, taken from a
     subset of the values from <errno.h> in the rstatus argument, if that was
     not given as a NULL pointer.  See the ERRORS section below for the
     possible values.

EXAMPLES
     The following example will always return a number in [1..99] range no
     matter what the input is, and warn if the conversion failed.

           int e;
           uintmax_t lval = strtou(buf, NULL, 0, 1, 99, &e);
           if (e)
                   warnc(e, "conversion of `%s' to a number failed, using %ju",
                       buf, lval);

ERRORS
     [ECANCELED]        The string did not contain any characters that were
                        converted.  If given endptr will be set to nptr.

     [EINVAL]           The base is not between 2 and 36 and nor is it the
                        special value 0.  If given endptr will be set to nptr.

     [ENOTSUP]          The string contained non-numeric characters that did
                        not get converted.  In this case, endptr points to the
                        first unconverted character.

     [ERANGE]           The given string was out of range; the value converted
                        has been clamped.  In this case, endptr points to the
                        terminating `\0' if the nptr string was fully
                        converted, or to the first unconverted character
                        otherwise.

     The validity of the provided base is checked first, and if that fails, no
     further processing is attempted.  The range check is more important than
     the unconverted characters check, and is given priority.  If a program
     needs to know if there were unconverted characters when an out of range
     number has been provided, it needs to supply and test endptr.

SEE ALSO
     atof(3), atoi(3), atol(3), atoll(3), strtod(3), strtoi(3), strtoumax(3),
     strtol(3), strtoll(3), strtoul(3), strtoull(3), warnc(3)

STANDARDS
     The strtou() and strtou_l() functions are a NetBSD extension.

HISTORY
     The strtou() function first appeared in NetBSD 7.  OpenBSD introduced the
     strtonum(3) function for the same purpose, but its interface makes it
     impossible to properly differentiate error conditions.

BUGS
     Ignores the current locale while doing the numeric conversion, only ASCII
     letters and digits are allowed, and no grouping characters.

NetBSD 11.99                     July 24, 2024                    NetBSD 11.99