fgetpos(S-osr5)

fgetpos -- gets and stores the current value of a stream's file position indicator

Syntax

cc . . . -lc

#include  <stdio.h>

int fgetpos(stream, pos)
FILE *stream;
fpos_t *pos;

Description

The fgetpos function gets the current value of streams file position indicator and stores it in the object to which pos points. The fsetpos function can later use information stored in pos to reset stream's pointer to its position when fgetpos was called.

Notes

The pos value is stored in an internal format and is intended for use only by the fgetpos and fsetpos functions.

Return value

If successful, the fgetpos function returns 0. If it fails, it returns a nonzero value and sets errno to one of the following manifest constants (defined in stdio.h):

EBADF: The specified stream is not a valid file handle or is not accessible.
EINVAL: The stream value is invalid.

Standards conformance

fgetpos is conformant with:

ANSI X3.159-1989 Programming Language -- C .

Example

   #include <stdio.h>
   
   FILE *stream;
   fpos_t position[];
   int val, i;
   char fcontents[13]; /* buffer for full contents of file1 */
   char writein1[14]= "Hello world!\n";
   char writein2[8]= "there.\n";
   

   main()
   {
           if ((stream = fopen("file1","w+")) == NULL)  /* open file1 */
           {
                   perror("fopen");
                   printf ("Trouble opening file\n");
           }
           else /* write in 1st string */
                   fwrite(writein1,sizeof(char),13,stream);
   

           position=0;
           fsetpos(stream, &position);         /*reset file to beginning */
   

           fread(fcontents, sizeof(char), 13, stream); /* read contents */
           printf("%s", fcontents);                    /* and print it */
   

           position=0;
           fsetpos(stream, &position);         /*reset file to beginning */
   

           fread(fcontents, sizeof(char), 5, stream); /* read "Hello" */
           if (fgetpos(stream, &position) != 0)  /* Save current position */
                   perror("fgetpos error");
   

           fread(fcontents, sizeof(char), 8, stream); /* read some more */
           if (fsetpos(stream, &position) != 0)  /* Return to saved position */
                   perror("fsetpos error");
   

           /* Overwrite file from this position with the word "there" */
   

           fwrite(writein2, sizeof(char), 8, stream);
   

           position=0;
           fsetpos(stream, &position);         /*reset file to beginning */
           fread(fcontents, sizeof(char), 13, stream);
           printf("%s", fcontents);                    /* print contents */
   

   }

This program opens a file named file1 and prints ``Hello world!'' It then outputs the file contents on screen. Next, it reads the first five characters in the file hello and calls fgetpos to find and save the file position pointer. After performing another read, the program calls fsetpos to restore the file pointer to the saved position.