File Positioning - GNU Octave
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#### 14.2.19 File Positioning

Three functions are available for setting and determining the position of the file pointer for a given file.

— Built-in Function: ftell (fid)

> Return the position of the file pointer as the number of characters from the beginning of the file fid.

> See also: fseek, fopen, fclose.

— Built-in Function: fseek (fid, offset, origin)

> Set the file pointer to any location within the file fid.

> The pointer is positioned offset characters from the origin, which may be one of the predefined variables `SEEK_CUR` (current position), `SEEK_SET` (beginning), or `SEEK_END` (end of file) or strings "cof", "bof" or "eof". If origin is omitted, `SEEK_SET` is assumed. The offset must be zero, or a value returned by `ftell` (in which case origin must be `SEEK_SET`).

> Return 0 on success and -1 on error.

> See also: ftell, fopen, fclose.

— Built-in Function: SEEK_SET ()
— Built-in Function: SEEK_CUR ()
— Built-in Function: SEEK_END ()

> Return the numerical value to pass to `fseek` to perform one of the following actions:

> `SEEK_SET`
>   Position file relative to the beginning.
> `SEEK_CUR`
>   Position file relative to the current position.
> `SEEK_END`
>   Position file relative to the end.

> See also: fseek.

— Built-in Function: frewind (fid)

> Move the file pointer to the beginning of the file fid, returning 0 for success, and -1 if an error was encountered. It is equivalent to `fseek (`fid`, 0, SEEK_SET)`.

The following example stores the current file position in the variable `marker`, moves the pointer to the beginning of the file, reads four characters, and then returns to the original position.

         marker = ftell (myfile);
         frewind (myfile);
         fourch = fgets (myfile, 4);
         fseek (myfile, marker, SEEK_SET);