fseek.3p (7011B)
- '\" et
- .TH FSEEK "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH PROLOG
- This manual page is part of the POSIX Programmer's Manual.
- The Linux implementation of this interface may differ (consult
- the corresponding Linux manual page for details of Linux behavior),
- or the interface may not be implemented on Linux.
- .\"
- .SH NAME
- fseek,
- fseeko
- \(em reposition a file-position indicator in a stream
- .SH SYNOPSIS
- .LP
- .nf
- #include <stdio.h>
- .P
- int fseek(FILE *\fIstream\fP, long \fIoffset\fP, int \fIwhence\fP);
- int fseeko(FILE *\fIstream\fP, off_t \fIoffset\fP, int \fIwhence\fP);
- .fi
- .SH DESCRIPTION
- The functionality described on this reference page is aligned with the
- ISO\ C standard. Any conflict between the requirements described here and the
- ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
- .P
- The
- \fIfseek\fR()
- function shall set the file-position indicator for the stream pointed
- to by
- .IR stream .
- If a read or write error occurs, the error indicator for the stream
- shall be set and
- \fIfseek\fR()
- fails.
- .P
- The new position, measured in bytes from the beginning of the file,
- shall be obtained by adding
- .IR offset
- to the position specified by
- .IR whence .
- The specified point is the beginning of the file for SEEK_SET, the
- current value of the file-position indicator for SEEK_CUR, or
- end-of-file for SEEK_END.
- .P
- If the stream is to be used with wide-character input/output functions,
- the application shall ensure that
- .IR offset
- is either 0 or a value returned by an earlier call to
- \fIftell\fR()
- on the same stream and
- .IR whence
- is SEEK_SET.
- .P
- A successful call to
- \fIfseek\fR()
- shall clear the end-of-file indicator for the stream and undo any
- effects of
- \fIungetc\fR()
- and
- \fIungetwc\fR()
- on the same stream. After an
- \fIfseek\fR()
- call, the next operation on an update stream may be either input or
- output.
- .P
- If the most recent operation, other than
- \fIftell\fR(),
- on a given stream is
- \fIfflush\fR(),
- the file offset in the underlying open file description shall be
- adjusted to reflect the location specified by
- \fIfseek\fR().
- .P
- The
- \fIfseek\fR()
- function shall allow the file-position indicator to be set beyond the
- end of existing data in the file. If data is later written at this
- point, subsequent reads of data in the gap shall return bytes with the
- value 0 until data is actually written into the gap.
- .P
- The behavior of
- \fIfseek\fR()
- on devices which are incapable of seeking is implementation-defined.
- The value of the file offset associated with such a device is
- undefined.
- .P
- If the stream is writable and buffered data had not been written to the
- underlying file,
- \fIfseek\fR()
- shall cause the unwritten data to be written to the file and shall mark
- the last data modification and last file status change timestamps
- of the file for update.
- .P
- In a locale with state-dependent encoding, whether
- \fIfseek\fR()
- restores the stream's shift state is implementation-defined.
- .P
- The
- \fIfseeko\fR()
- function shall be equivalent to the
- \fIfseek\fR()
- function except that the
- .IR offset
- argument is of type
- .BR off_t .
- .SH "RETURN VALUE"
- The
- \fIfseek\fR()
- and
- \fIfseeko\fR()
- functions shall return 0 if they succeed.
- .P
- Otherwise, they shall return \-1 and set
- .IR errno
- to indicate the error.
- .SH ERRORS
- The
- \fIfseek\fR()
- and
- \fIfseeko\fR()
- functions shall fail if,
- either the
- .IR stream
- is unbuffered or the
- .IR stream 's
- buffer needed to be flushed, and the call to
- \fIfseek\fR()
- or
- \fIfseeko\fR()
- causes an underlying
- \fIlseek\fR()
- or
- \fIwrite\fR()
- to be invoked, and:
- .TP
- .BR EAGAIN
- The O_NONBLOCK flag is set for the file descriptor and the thread
- would be delayed in the write operation.
- .TP
- .BR EBADF
- The file descriptor underlying the stream file is not open for writing
- or the stream's buffer needed to be flushed and the file is not open.
- .TP
- .BR EFBIG
- An attempt was made to write a file that exceeds the maximum file size.
- .TP
- .BR EFBIG
- An attempt was made to write a file that exceeds the file size
- limit of the process.
- .TP
- .BR EFBIG
- The file is a regular file and an attempt was made to write at or
- beyond the offset maximum associated with the corresponding stream.
- .TP
- .BR EINTR
- The write operation was terminated due to the receipt of a signal,
- and no data was transferred.
- .TP
- .BR EINVAL
- The
- .IR whence
- argument is invalid. The resulting file-position indicator would be
- set to a negative value.
- .TP
- .BR EIO
- A physical I/O error has occurred, or the process is a member of a
- background process group attempting to perform a
- \fIwrite\fR()
- to its controlling terminal, TOSTOP is set, the calling thread is not
- blocking SIGTTOU, the process is not ignoring SIGTTOU, and the process
- group of the process is orphaned.
- This error may also be returned under implementation-defined conditions.
- .TP
- .BR ENOSPC
- There was no free space remaining on the device containing the file.
- .TP
- .BR EOVERFLOW
- For
- \fIfseek\fR(),
- the resulting file offset would be a value which cannot be represented
- correctly in an object of type
- .BR long .
- .TP
- .BR EOVERFLOW
- For
- \fIfseeko\fR(),
- the resulting file offset would be a value which cannot be represented
- correctly in an object of type
- .BR off_t .
- .TP
- .BR EPIPE
- An attempt was made to write to a pipe or FIFO that is not open for
- reading by any process; a SIGPIPE
- signal shall also be sent to the thread.
- .TP
- .BR ESPIPE
- The file descriptor underlying
- .IR stream
- is associated with a pipe, FIFO, or socket.
- .P
- The
- \fIfseek\fR()
- and
- \fIfseeko\fR()
- functions may fail if:
- .TP
- .BR ENXIO
- A request was made of a nonexistent device, or the request was outside
- the capabilities of the device.
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- None.
- .SH "APPLICATION USAGE"
- None.
- .SH RATIONALE
- None.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "Section 2.5" ", " "Standard I/O Streams",
- .IR "\fIfopen\fR\^(\|)",
- .IR "\fIfsetpos\fR\^(\|)",
- .IR "\fIftell\fR\^(\|)",
- .IR "\fIgetrlimit\fR\^(\|)",
- .IR "\fIlseek\fR\^(\|)",
- .IR "\fIrewind\fR\^(\|)",
- .IR "\fIulimit\fR\^(\|)",
- .IR "\fIungetc\fR\^(\|)",
- .IR "\fIwrite\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<stdio.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, Standard for Information Technology
- -- Portable Operating System Interface (POSIX), The Open Group Base
- Specifications Issue 7, 2018 Edition,
- Copyright (C) 2018 by the Institute of
- Electrical and Electronics Engineers, Inc and The Open Group.
- In the event of any discrepancy between this version and the original IEEE and
- The Open Group Standard, the original IEEE and The Open Group Standard
- is the referee document. The original Standard can be obtained online at
- http://www.opengroup.org/unix/online.html .
- .PP
- Any typographical or formatting errors that appear
- in this page are most likely
- to have been introduced during the conversion of the source files to
- man page format. To report such errors, see
- https://www.kernel.org/doc/man-pages/reporting_bugs.html .