file_ptr

    A pointer to the file to which the output is directed.

 format_spec

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

  . . .

    Optional expressions whose resultant types correspond to
    conversion specifications given in the format specification.

    If no conversion specifications are given, the output sources can
    be omitted. Otherwise, the function calls must have exactly as
    many output sources as there are conversion specifications, and
    the conversion specifications must match the types of the output
    sources.

    Conversion specifications are matched to output sources in left-
    to-right order. Any excess output sources are ignored.