Prints formatted output based on an argument list.

    This function is supported on OpenVMS Integrity servers and
    Alpha only.

    Format

      #include  <stdio.h>

      int vsnprintf  (char *str, size_t n, const char *format,
                     va_list ap);

1 - Arguments

 str

    A pointer to a string that will receive the formatted output.

 format

    A pointer to a character string that contains the format
    specification.

 ap

    A list of expressions whose resultant types correspond to the
    conversion specifications given in the format specifications.

2 - Description

    The vsnprintf function is the same as the snprintf function, but
    instead of being called with a variable number of arguments, it
    is called with an argument list that has been initialized by va_
    start (and possibly with subsequent va_arg calls).

    This function does not invoke the va_end macro. Because the
    function invokes the va_arg macro, the value of ap after the
    return is unspecified.

    Applications using vsnprintf should call va_end(ap) afterwards to
    clean up.

3 - Return Values

    x                  The number of bytes (excluding the terminating
                       null byte) that would be written to str if n
                       is sufficiently large.
    Negative value     Indicates an output error occurred. The
                       function sets errno. For a list of possible
                       errno values set, see fprintf.