man-pages/man3p/fdopen.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "FDOPEN" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" fdopen 
.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
fdopen \- associate a stream with a file descriptor
.SH SYNOPSIS
.LP
\fB#include <stdio.h>
.br
.sp
FILE *fdopen(int\fP \fIfildes\fP\fB, const char *\fP\fImode\fP\fB);
\fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIfdopen\fP() function shall associate a stream with a file descriptor.
.LP
The \fImode\fP argument is a character string having one of the following
values:
.TP 7
\fIr\fP\ or\ \fIrb\fP
Open a file for reading.
.TP 7
\fIw\fP\ or\ \fIwb\fP
Open a file for writing.
.TP 7
\fIa\fP\ or\ \fIab\fP
Open a file for writing at end-of-file.
.TP 7
\fIr\fP+\ or\ \fIrb\fP+\ or\ \fIr\fP+\fIb\fP
Open a file for update (reading and writing).
.TP 7
\fIw\fP+\ or\ \fIwb\fP+\ or\ \fIw\fP+\fIb\fP
Open a file for update (reading and writing).
.TP 7
\fIa\fP+\ or\ \fIab\fP+\ or\ \fIa\fP+\fIb\fP
Open a file for update (reading and writing) at end-of-file.
.sp
.LP
The meaning of these flags is exactly as specified in \fIfopen\fP(),
except that modes
beginning with \fIw\fP shall not cause truncation of the file.
.LP
Additional values for the \fImode\fP argument may be supported by
an implementation.
.LP
The application shall ensure that the mode of the stream as expressed
by the \fImode\fP argument is allowed by the file access
mode of the open file description to which \fIfildes\fP refers. The
file position indicator associated with the new stream is set
to the position indicated by the file offset associated with the file
descriptor.
.LP
The error and end-of-file indicators for the stream shall be cleared.
The \fIfdopen\fP() function may cause the \fIst_atime\fP
field of the underlying file to be marked for update.
.LP
If \fIfildes\fP refers to a shared memory object, the result of the
\fIfdopen\fP() function is unspecified. 
.LP
If \fIfildes\fP refers to a typed memory object, the result of the
\fIfdopen\fP() function is unspecified. 
.LP
The \fIfdopen\fP() function shall preserve the offset maximum previously
set for the open file description corresponding to
\fIfildes\fP.
.SH RETURN VALUE
.LP
Upon successful completion, \fIfdopen\fP() shall return a pointer
to a stream; otherwise, a null pointer shall be returned and
\fIerrno\fP set to indicate the error.
.SH ERRORS
.LP
The \fIfdopen\fP() function may fail if:
.TP 7
.B EBADF
The \fIfildes\fP argument is not a valid file descriptor.
.TP 7
.B EINVAL
The \fImode\fP argument is not a valid mode.
.TP 7
.B EMFILE
{FOPEN_MAX} streams are currently open in the calling process.
.TP 7
.B EMFILE
{STREAM_MAX} streams are currently open in the calling process.
.TP 7
.B ENOMEM
Insufficient space to allocate a buffer.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
File descriptors are obtained from calls like \fIopen\fP(), \fIdup\fP(),
\fIcreat\fP(), or \fIpipe\fP(), which open files but do not return
streams.
.SH RATIONALE
.LP
The file descriptor may have been obtained from \fIopen\fP(), \fIcreat\fP(),
\fIpipe\fP(), \fIdup\fP(), or \fIfcntl\fP(); inherited through \fIfork\fP()
or \fIexec\fP; or perhaps obtained by
implementation-defined means, such as the 4.3 BSD \fIsocket\fP() call.
.LP
The meanings of the \fImode\fP arguments of \fIfdopen\fP() and \fIfopen\fP()
differ.
With \fIfdopen\fP(), open for write (\fIw\fP or \fIw+\fP) does not
truncate, and append (\fIa\fP or \fIa+\fP) cannot create
for writing. The \fImode\fP argument formats that include \fIa b\fP
are allowed for consistency with the ISO\ C standard
function \fIfopen\fP(). The \fIb\fP has no effect on the resulting
stream. Although not
explicitly required by this volume of IEEE\ Std\ 1003.1-2001, a good
implementation of append (\fIa\fP) mode would cause
the O_APPEND flag to be set.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIInteraction of File Descriptors and Standard I/O Streams\fP, \fIfclose\fP()
, \fIfopen\fP(), \fIopen\fP(), the Base
Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<stdio.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .