FSEEK(3S) (C Programming Language Utilities) FSEEK(3S)
NAME
fseek, rewind, ftell - reposition a file pointer in a stream
SYNOPSIS
#include <stdio.h>
int fseek (stream, offset, ptrname)
FILE *stream;
long offset;
int ptrname;
void rewind (stream)
FILE *stream;
long ftell (stream)
FILE *stream;
DESCRIPTION
fseek sets the position of the next input or output
operation on the stream. 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 as ptrname
has the value 0, 1, or 2.
Rewind(stream) is equivalent to fseek(stream, 0L, 0), except
that no value is returned.
fseek and rewind undo any effects of ungetc(3S).
After fseek or rewind, the next operation on a file opened
for update may be either input or output.
Ftell returns the offset of the current byte relative to the
beginning of the file associated with the named stream.
SEE ALSO
lseek(2), fopen(3S), popen(3S), stdio(3S), ungetc(3S).
DIAGNOSTICS
fseek returns non-zero for improper seeks, otherwise zero.
Page 1 May 1989
FSEEK(3S) (C Programming Language Utilities) FSEEK(3S)
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(3S).
WARNING
Although on UniSoft SYSTEM V an offset returned by ftell is
measured in bytes, and it is permissible to seek to
positions relative to that offset, portability to non-UNIX
systems 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.
Page 2 May 1989