#include <string.h>
#include <stdio.h>

/*
 ---------------------------
 size_t fread(void *ptr, size_t size, size_t n, FILE *stream);
Description
 Reads data from a stream.
 fread reads n items of data each of length size bytes from the given input
 stream into a block pointed to by ptr. The total number of bytes read
 is (n * size).
Return Value
 On success fread returns the number of items (not bytes) actually read.
 On end-of-file or error it returns a short count (possibly 0).

 ---------------------------
size_t fwrite(const void *ptr, size_t size, size_t n, FILE *stream);
Description
 Writes to a stream.
 fwrite appends n items of data each of length size bytes to the given output
 file. The data written begins at ptr. The total number of bytes written
 is (n x size). ptr in the declarations is a pointer to any object.
Return Value
 On successful completion fwrite returns the number of items (not bytes)
 actually written. On error it returns a short count.

 ---------------------------
 FILE *fopen(const char *filename, const char *mode);
Description
 Opens a stream.
 fopen opens the file named by filename and associates a stream with it. fopen
 returns a pointer to be used to identify the stream in subsequent operations.
 The mode string used in calls to fopen is one of the following values:
Value	Description

r	Open for reading only.
w	Create for writing. If a file by that name already exists, it will
        be overwritten.
a	Append; open for writing at end-of-file or create for writing if the
        file does not exist.
r+	Open an existing file for update (reading and writing).
w+	Create a new file for update (reading and writing). If a file by that
        name already exists, it will be overwritten.
a+	Open for append; open (or create if the file does not exist) for update
        at the end of the file.

 ---------------------------
 int fseek(FILE *stream, long offset, int whence);
Description
 Repositions a file pointer on a stream.
 fseek sets the file pointer associated with stream to a new position that is
 offset bytes from the file location given by whence. For text mode streams
 offset should be 0 or a value returned by ftell.
 whence must be one of the values 0. 1, or 2 which represent three symbolic
 constants (defined in stdio.h) as follows:
Constant	whence	File location
SEEK_SET	0	File beginning
SEEK_CUR	1	Current file pointer position
SEEK_END	2	End-of-file

 fseek discards any character pushed back using ungetc. fseek is used with
 stream I/O; for file handle I/O use lseek.
 After fseek the next operation on an update file can be either input or output.
*/

int main(void)
{
   FILE *stream;
   char msg[] = "this is a test";
   char buf[20];

   if ((stream = fopen("dummy.file", "w+"))
       == NULL)
   {
      fprintf(stderr, "Cannot open output file.\n");
      return 1;
   }

   /* write some data to the file */
   fwrite(msg, strlen(msg)+1, 1, stream);

   /* seek to the beginning of the file */
   fseek(stream, SEEK_SET, 0);

   /* read the data and display it */

   fread(buf, strlen(msg)+1, 1, stream);
   printf("%s\n", buf);

   fclose(stream);
   return 0;
}