114 \fBfseek\fR(3C). If two separate processes open the same file for append, each
 115 process may write freely to the file without fear of destroying output being
 116 written by the other.  The output from the two processes will be intermixed in
 117 the file in the order in which it is written.
 118 .sp
 119 .LP
 120 When a file is opened with update mode (\fB+\fR as the second or third
 121 character in the \fImode\fR argument), both input and output may be performed
 122 on the associated stream. However, output must not be directly followed by
 123 input without an intervening call to \fBfflush\fR(3C) or to a file positioning
 124 function ( \fBfseek\fR(3C), \fBfsetpos\fR(3C) or \fBrewind\fR(3C)), and input
 125 must not be directly followed by output without an intervening call to a file
 126 positioning function, unless the input operation encounters end-of-file.
 127 .sp
 128 .LP
 129 When opened, a stream is fully buffered if and only if it can be determined not
 130 to refer to an interactive device. The error and end-of-file indicators for the
 131 stream are cleared.
 132 .sp
 133 .LP
 134 If \fImode\fR begins with \fIw\fR or \fBa\fR and the file did not previously
 135 exist, upon successful completion, \fBfopen()\fR function will mark for update
 136 the \fBst_atime\fR, \fBst_ctime\fR and \fBst_mtime\fR fields of the file and
 137 the \fBst_ctime\fR and \fBst_mtime\fR fields of the parent directory.
 138 .sp
 139 .LP
 140 If \fImode\fR begins with \fIw\fR and the file did previously exist, upon
 141 successful completion, \fBfopen()\fR will mark for update the \fBst_ctime\fR
 142 and \fBst_mtime\fR fields of the file.  The \fBfopen()\fR function will
 143 allocate a file descriptor as \fBopen\fR(2) does.
 144 .sp
 145 .LP
 146 Normally, 32-bit applications return an \fBEMFILE\fR error when attempting to
 147 associate a stream with a file accessed by a file descriptor with a value
 148 greater than 255. If the last character of \fImode\fR is \fBF\fR, 32-bit
 149 applications will be allowed to associate a stream with a file accessed by a
 150 file descriptor with a value greater than 255. A \fBFILE\fR pointer obtained in
 151 this way must never be used by any code that might directly access fields in
 152 the \fBFILE\fR structure. If the fields in the \fBFILE\fR structure are used
 153 directly by 32-bit applications when the last character of mode is \fBF\fR,
 154 data corruption could occur. See the USAGE section of this manual page and the
 155 \fBenable_extended_FILE_stdio\fR(3C) manual page for other options for enabling
 156 the extended FILE facility.
 157 .sp
 158 .LP
 159 In 64-bit applications, the last character of \fImode\fR is silently ignored if
 160 it is \fBF\fR.  64-bit applications are always allowed to associate a stream

 114 \fBfseek\fR(3C). If two separate processes open the same file for append, each
 115 process may write freely to the file without fear of destroying output being
 116 written by the other.  The output from the two processes will be intermixed in
 117 the file in the order in which it is written.
 118 .sp
 119 .LP
 120 When a file is opened with update mode (\fB+\fR as the second or third
 121 character in the \fImode\fR argument), both input and output may be performed
 122 on the associated stream. However, output must not be directly followed by
 123 input without an intervening call to \fBfflush\fR(3C) or to a file positioning
 124 function ( \fBfseek\fR(3C), \fBfsetpos\fR(3C) or \fBrewind\fR(3C)), and input
 125 must not be directly followed by output without an intervening call to a file
 126 positioning function, unless the input operation encounters end-of-file.
 127 .sp
 128 .LP
 129 When opened, a stream is fully buffered if and only if it can be determined not
 130 to refer to an interactive device. The error and end-of-file indicators for the
 131 stream are cleared.
 132 .sp
 133 .LP
 134 If \fImode\fR begins with \fBw\fR or \fBa\fR and the file did not previously
 135 exist, upon successful completion, \fBfopen()\fR function will mark for update
 136 the \fBst_atime\fR, \fBst_ctime\fR and \fBst_mtime\fR fields of the file and
 137 the \fBst_ctime\fR and \fBst_mtime\fR fields of the parent directory.
 138 .sp
 139 .LP
 140 If \fImode\fR begins with \fBw\fR and the file did previously exist, upon
 141 successful completion, \fBfopen()\fR will mark for update the \fBst_ctime\fR
 142 and \fBst_mtime\fR fields of the file.  The \fBfopen()\fR function will
 143 allocate a file descriptor as \fBopen\fR(2) does.
 144 .sp
 145 .LP
 146 Normally, 32-bit applications return an \fBEMFILE\fR error when attempting to
 147 associate a stream with a file accessed by a file descriptor with a value
 148 greater than 255. If the last character of \fImode\fR is \fBF\fR, 32-bit
 149 applications will be allowed to associate a stream with a file accessed by a
 150 file descriptor with a value greater than 255. A \fBFILE\fR pointer obtained in
 151 this way must never be used by any code that might directly access fields in
 152 the \fBFILE\fR structure. If the fields in the \fBFILE\fR structure are used
 153 directly by 32-bit applications when the last character of mode is \fBF\fR,
 154 data corruption could occur. See the USAGE section of this manual page and the
 155 \fBenable_extended_FILE_stdio\fR(3C) manual page for other options for enabling
 156 the extended FILE facility.
 157 .sp
 158 .LP
 159 In 64-bit applications, the last character of \fImode\fR is silently ignored if
 160 it is \fBF\fR.  64-bit applications are always allowed to associate a stream