fseek(3S)            STANDARD I/O FUNCTIONS             fseek(3S)



NAME
     fseek, rewind, ftell - reposition a file pointer in a stream

SYNOPSIS
     #include <stdio.h>

     int fseek (FILE *stream, long offset, int ptrname);

     void rewind (FILE *stream);

     long ftell (FILE *stream);

DESCRIPTION
     fseek sets the position of the next input or  output  opera-
     tion  on  the stream [see intro(3)].  The new position is at
     the signed distance offset bytes from  the  beginning,  from
     the current position, or from the end of the file, according
     to a  ptrname  value  of  SEEKSET,  SEEKCUR,  or  SEEKEND
     (defined in stdio.h) as follows:

     SEEKSET    set position equal to offset bytes.

     SEEKCUR    set position to current location plus offset.

     SEEKEND    set position to EOF plus offset.   fseek  allows
                 the file position indicator to be set beyond the
                 end of the existing data in the file.   If  data
                 is later written at this point, subsequent reads
                 of data in the gap will return zero  until  data
                 is  actually  written  into  the gap.  fseek, by
                 itself, does not extend the size of the file.

     rewind (stream) is equivalent to:

          (void) fseek (stream, 0L, SEEKSET);

     except that  rewind  also  clears  the  error  indicator  on
     stream.

     fseek and rewind  clear  the  EOF  indicator  and  undo  any
     effects  of  ungetc  on  stream.  After fseek or rewind, the
     next operation on a file opened for  update  may  be  either
     input or output.

     If stream is writable and buffered data has not been written
     to the underlying file, fseek and rewind cause the unwritten
     data to be written to the file.

     ftell returns the offset of the current byte relative to the
     beginning of the file associated with the named stream.





          Last change: C Programming Language Utilities         1

fseek(3S)            STANDARD I/O FUNCTIONS             fseek(3S)



SEE ALSO
     lseek(2),   write(2),   fopen(3S),   popen(3S),   stdio(3S),
     ungetc(3S).

DIAGNOSTICS
     fseek returns -1 for improper  seeks,  otherwise  zero.   An
     improper  seek  can be, for example, an fseek done on a file
     that has not been opened via fopen; in particular, fseek may
     not  be  used  on  a terminal or on a file opened via popen.
     After a stream is closed, no further operations are  defined
     on that stream.

NOTES
     Although on the UNIX system an offset returned by  ftell  is
     measured  in  bytes,  and it is permissible to seek to posi-
     tions relative to that offset, portability to non-UNIX  sys-
     tems  requires  that  an  offset  be used by fseek directly.
     Arithmetic may not meaningfully  be  performed  on  such  an
     offset, which is not necessarily measured in bytes.




































          Last change: C Programming Language Utilities         2