TYPE buffer[count];
fwrite( buffer, sizeof(TYPE), count, stream );

//=================

fread( buffer, sizeof(TYPE), count, stream ); // TYPE does not matter
buffer[3]; // now data is read according to TYPE encoding


// this works on 1 element
TYPE value;     // array[1] 
TYPE array[1];  
fwrite( &value, sizeof(TYPE), 1, stream );

splitter
--------

+--------------------------+
|    input file            | 256 Gb   HARDDRIVE
|                          |
+--------------------------+

// +------------+
// |  chunk1    | BUFFER  =  CHUNK to much space 
// |            |
// +------------+

+--+
|  | 4K buffer
+--+

buffer in memory




+------------++------------+
|  chunk1    || chunk2     |         HARDDRIVE
|            ||            |
+------------++------------+

copy on 2*128Gb flash-drives

+--------------------------+
|11223344556|677..           | 256 Gb   HARDDRIVE
+--------------------------+
 |
 V
+--+
|67| 4K buffer
+--+
 |
 V

+-----------+ +
|11223344556| |67.....
+-----------+ +

DO NOT USE:
ftell/fseek
arbitrary sized buffer <=4K
remove

1122 - input
split into 2-byte file
|11|
|22|
||   empty file