1FSEEK(3P) POSIX Programmer's Manual FSEEK(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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12 fseek, fseeko - reposition a file-position indicator in a stream
13
15 #include <stdio.h>
16 int fseek(FILE *stream, long offset, int whence);
18 int fseeko(FILE *stream, off_t offset, int whence);
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24 The fseek() function shall set the file-position indicator for the
25 stream pointed to by stream. If a read or write error occurs, the error
26 indicator for the stream shall be set and fseek() fails.
27 The new position, measured in bytes from the beginning of the file,
29 shall be obtained by adding offset to the position specified by whence.
30 The specified point is the beginning of the file for SEEK_SET, the cur‐
31 rent value of the file-position indicator for SEEK_CUR, or end-of-file
32 for SEEK_END.
33 If the stream is to be used with wide-character input/output functions,
35 the application shall ensure that offset is either 0 or a value
36 returned by an earlier call to ftell() on the same stream and whence is
37 SEEK_SET.
38 A successful call to fseek() shall clear the end-of-file indicator for
40 the stream and undo any effects of ungetc() and ungetwc() on the same
41 stream. After an fseek() call, the next operation on an update stream
42 may be either input or output.
43 If the most recent operation, other than ftell(), on a given stream is
45 fflush(), the file offset in the underlying open file description shall
46 be adjusted to reflect the location specified by fseek().
47 The fseek() function shall allow the file-position indicator to be set
49 beyond the end of existing data in the file. If data is later written
50 at this point, subsequent reads of data in the gap shall return bytes
51 with the value 0 until data is actually written into the gap.
52 The behavior of fseek() on devices which are incapable of seeking is
54 implementation-defined. The value of the file offset associated with
55 such a device is undefined.
56 If the stream is writable and buffered data had not been written to the
58 underlying file, fseek() shall cause the unwritten data to be written
59 to the file and shall mark the st_ctime and st_mtime fields of the file
60 for update.
61 In a locale with state-dependent encoding, whether fseek() restores the
63 stream's shift state is implementation-defined.
64 The fseeko() function shall be equivalent to the fseek() function
66 except that the offset argument is of type off_t.
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69 The fseek() and fseeko() functions shall return 0 if they succeed.
70 Otherwise, they shall return -1 and set errno to indicate the error.
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74 The fseek() and fseeko() functions shall fail if, either the stream
75 is unbuffered or the stream's buffer needed to be flushed, and the call
76 to fseek() or fseeko() causes an underlying lseek() or write() to be
77 invoked, and:
78 EAGAIN The O_NONBLOCK flag is set for the file descriptor and the
80 process would be delayed in the write operation.
81 EBADF The file descriptor underlying the stream file is not open for
83 writing or the stream's buffer needed to be flushed and the file
84 is not open.
85 EFBIG An attempt was made to write a file that exceeds the maximum
87 file size.
88 EFBIG An attempt was made to write a file that exceeds the process'
90 file size limit.
91 EFBIG The file is a regular file and an attempt was made to write at
93 or beyond the offset maximum associated with the corresponding
94 stream.
95 EINTR The write operation was terminated due to the receipt of a sig‐
97 nal, and no data was transferred.
98 EINVAL The whence argument is invalid. The resulting file-position
100 indicator would be set to a negative value.
101 EIO A physical I/O error has occurred, or the process is a member of
103 a background process group attempting to perform a write() to
104 its controlling terminal, TOSTOP is set, the process is neither
105 ignoring nor blocking SIGTTOU, and the process group of the
106 process is orphaned. This error may also be returned under
107 implementation-defined conditions.
108 ENOSPC There was no free space remaining on the device containing the
110 file.
111 ENXIO A request was made of a nonexistent device, or the request was
113 outside the capabilities of the device.
114 EOVERFLOW
116 For fseek(), the resulting file offset would be a value which
117 cannot be represented correctly in an object of type long.
118 EOVERFLOW
120 For fseeko(), the resulting file offset would be a value which
121 cannot be represented correctly in an object of type off_t.
122 EPIPE An attempt was made to write to a pipe or FIFO that is not open
124 for reading by any process; a SIGPIPE signal shall also be sent
125 to the thread.
126 ESPIPE The file descriptor underlying stream is associated with a pipe
128 or FIFO.
129 The following sections are informative.
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134 None.
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137 None.
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140 None.
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143 None.
144
146 fopen(), fsetpos(), ftell(), getrlimit(), lseek(), rewind(), ulimit(),
147 ungetc(), write(), the Base Definitions volume of IEEE Std 1003.1-2001,
148 <stdio.h>
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151 Portions of this text are reprinted and reproduced in electronic form
152 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
153 -- Portable Operating System Interface (POSIX), The Open Group Base
154 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
155 Electrical and Electronics Engineers, Inc and The Open Group. In the
156 event of any discrepancy between this version and the original IEEE and
157 The Open Group Standard, the original IEEE and The Open Group Standard
158 is the referee document. The original Standard can be obtained online
159 at http://www.opengroup.org/unix/online.html .
160IEEE/The Open Group 2003 FSEEK(3P)