.. _file_IO:

File I/O
========

- 
   Objective: Read and write to/from files like what we have done from
   the terminal.

-  Need to open a file, perform I/O, and then close the file.

- 
   To do this we need the notion of a *file descriptor*, which is our
   means of accessing the file.

-  The file descriptor is a pointer of type (FILE \*), which is a pointer to
   a data structure. See :ref:`fileIO` for more information.

- 
   `fopen("filename", "[rw]")` is the function we will use for opening
   files. See :ref:`fopen` for more information.

- 
   With an open file, we can use :func:`fscanf()`, :func:`fprintf()`, 
   :func:`fgets()` and other file I/0 functions.

-  We use `fclose( FILE * )` to close an open file.

- 
   Don't worry if you find this confusing at this time. We will cover
   file I/O in much more detail later.


File I/O examples
-----------------

    ::

        FILE *fin, *fout;
        char buff[SIZE];
        
        fin = fopen( "filename", "r" ); /* filename could be supplied by a
                                           string instead of a constant. */
        fout = fopen( "filename", "w" );
        
        fgets( buff, SIZE, fin );  
        fscanf( fin, "format", ...);
        
        fprintf( fout, "format", ...);
        
        fclose(fin);
        fclose(fout);

Now complete :ref:`hw5`.