FSEEK(3S-SVR4)      RISC/os Reference Manual       FSEEK(3S-SVR4)



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 SEEK_SET, SEEK_CUR, or SEEK_END
     (defined in stdio.h) as follows:

     SEEK_SET    set position equal to offset bytes.

     SEEK_CUR    set position to current location plus offset.

     SEEK_END    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, SEEK_SET);

     except that rewind also clears the error indicator on
     stream.

     fseek and rewind clear the EOF indicator and undo any
     effects of ungetc(3S) 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.




                        Printed 11/19/92                   Page 1

FSEEK(3S-SVR4)      RISC/os Reference Manual       FSEEK(3S-SVR4)



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.




































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