FILE - a structure containing the information about a file or text stream needed to perform 

input or output operations on it, including:
=> a file descriptor, the current stream position,
=> an end-of-file indicator, 
=> an error indicator, 
=> a pointer to the stream's buffer, if applicable

fpos_t - a non-array type capable of uniquely identifying the position of every byte in a file.
size_t - an unsigned integer type which is the type of the result of the sizeof operator.