The type size_t is defined in the header file <stdio.h> as
    follows:

    typedef unsigned int size_t

    The writing begins at the current location in the file. The items
    are written from storage beginning at the location given by the
    first argument. You must also specify the size of an item, in
    bytes.

    If the file pointed to by file_ptr is a record file, the fwrite
    function outputs at least number_items records, each of length
    size_of_item.