Reads formatted input based on an argument list.
    Format
      #include  <stdio.h>
      int vscanf  (const char *format, va_list ap);
1 – Arguments
 format
    A pointer to the string containing the format specification.
 ap
    A list of expressions whose resultant types correspond to the
    conversion specifications given in the format specifications.
2 – Description
    The vscanf function is the same as the scanf function except that
    instead of being called with a variable number of arguments, it
    is called with an argument list (ap) that has been initialized by
    the va_start macro (and possibly with subsequent va_arg calls).
    For more information about format and conversion specifications
    and their corresponding arguments, see the "Understanding Input
    and Output" chapter of the HP C RTL Reference Manual.
    See also scanf, vfscanf, and vsscanf.
3 – Return Values
    n                  The number of successfully matched and
                       assigned input items.
    EOF                Indicates that a read error occurred before
                       any conversion. The function sets errno. For a
                       list of the values set by this function, see
                       vfscanf.