When working with stream oriented data file,the first step is to establish a buffer area,where information is temporarily stored while being transferred between computers memory and data file.The buffer area can be established by declaring a file pointer.

The file pointer is the common thread that unites the buffered I/O systsm. A file pinter is a pointer to information that defines various things about the file,

including its name, status, and the current position of the file. In essence, the file pointer identifies a specific disk file and is used by the associated stream to direct the operation of the buffered I/O functions. A file pointer is a pointer variable of type FILE that is defined in stdio.h.file pointer variable can be declared as :

FILE *fp;

Where FILE is a special structure that establishes the buffer area, fp is a pointer variable that indicates the beginning of the buffer area.

The file stream structure FILE defined in DOS is shown below. It is not a good practice to use the members of the FILE structure.

Typedef struct
{
    Int level;                   /*fill/empty level of buffer*/
    Unsigned flags;              /*File status flags */
    Char fd;                     /*File descriptor (handle)*/
    Unsigned char hold;          /*ungetc char if no buffer*/
    Int bsize;                   /*Buffer size */
    Unsigned char_FAR *buffer;   /*Data transfer buffer */
    Unsigned char_FAR *curp;     /*Current active pointer */
    Unsigned istemp;             /*Temporary file indicator*/
    Short token;                 /*Used for validity checking*/
}FILE;                       /*This is the FILE object*/

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