'\" et

.TH FDOPEN "3P" 2013 "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

fdopen

\(em associate a stream with a file descriptor

.SH SYNOPSIS

.LP

.nf

#include <stdio.h>

.P

FILE *fdopen(int \fIfildes\fP, const char *\fImode\fP);

.fi

.SH DESCRIPTION

The

\fIfdopen\fR()

function shall associate a stream with a file descriptor.

.P

The

.IR mode

argument is a character string having one of the following values:

.IP "\fIr\fP\ or\ \fIrb\fP" 14

Open a file for reading.

.IP "\fIw\fP\ or\ \fIwb\fP" 14

Open a file for writing.

.IP "\fIa\fP\ or\ \fIab\fP" 14

Open a file for writing at end-of-file.

.IP "\fIr\fP+\ or\ \fIrb\fP+\ or\ \fIr\fP+\fIb\fP" 14

Open a file for update (reading and writing).

.IP "\fIw\fP+\ or\ \fIwb\fP+\ or\ \fIw\fP+\fIb\fP" 14

Open a file for update (reading and writing).

.IP "\fIa\fP+\ or\ \fIab\fP+\ or\ \fIa\fP+\fIb\fP" 14

Open a file for update (reading and writing) at end-of-file.

.P

The meaning of these flags is exactly as specified in

\fIfopen\fR(),

except that modes beginning with

.IR w

shall not cause truncation of the file.

.P

Additional values for the

.IR mode

argument may be supported by an implementation.

.P

The application shall ensure that the mode of the stream as expressed

by the

.IR mode

argument is allowed by the file access mode of the open file

description to which

.IR fildes

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.

.P

The error and end-of-file indicators for the stream shall be cleared.

The

\fIfdopen\fR()

function may cause the last data access timestamp of the underlying

file to be marked for update.

.P

If

.IR fildes

refers to a shared memory object, the result of the

\fIfdopen\fR()

function is unspecified.

.P

If

.IR fildes

refers to a typed memory object, the result of the

\fIfdopen\fR()

function is unspecified.

.P

The

\fIfdopen\fR()

function shall preserve the offset maximum previously set for the

open file description corresponding to

.IR fildes .

.SH "RETURN VALUE"

Upon successful completion,

\fIfdopen\fR()

shall return a pointer to a stream; otherwise, a null pointer shall be

returned and

.IR errno

set to indicate the error.

.SH ERRORS

The

\fIfdopen\fR()

function shall fail if:

.TP

.BR EMFILE

{STREAM_MAX}

streams are currently open in the calling process.

.P

The

\fIfdopen\fR()

function may fail if:

.TP

.BR EBADF

The

.IR fildes

argument is not a valid file descriptor.

.TP

.BR EINVAL

The

.IR mode

argument is not a valid mode.

.TP

.BR EMFILE

{FOPEN_MAX}

streams are currently open in the calling process.

.TP

.BR ENOMEM

Insufficient space to allocate a buffer.

.LP

.IR "The following sections are informative."

.SH EXAMPLES

None.

.SH "APPLICATION USAGE"

File descriptors are obtained from calls like

\fIopen\fR(),

\fIdup\fR(),

\fIcreat\fR(),

or

\fIpipe\fR(),

which open files but do not return streams.

.SH RATIONALE

The file descriptor may have been obtained from

\fIopen\fR(),

\fIcreat\fR(),

\fIpipe\fR(),

\fIdup\fR(),

\fIfcntl\fR(),

or

\fIsocket\fR();

inherited through

\fIfork\fR(),

\fIposix_spawn\fR(),

or

.IR exec ;

or perhaps obtained by other means.

.P

The meanings of the

.IR mode

arguments of

\fIfdopen\fR()

and

\fIfopen\fR()

differ. With

\fIfdopen\fR(),

open for write (\fIw\fP or \fIw+\fP) does not truncate, and append

(\fIa\fP or \fIa+\fP) cannot create for writing. The

.IR mode

argument formats that include a \fIb\fP are allowed for consistency

with the ISO\ C standard function

\fIfopen\fR().

The \fIb\fP has no effect on the resulting stream. Although not

explicitly required by this volume of POSIX.1\(hy2008, a good implementation of append (\fIa\fP)

mode would cause the O_APPEND flag to be set.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "Section 2.5.1" ", " "Interaction of File Descriptors and Standard I/O Streams",

.IR "\fIfclose\fR\^(\|)",

.IR "\fIfmemopen\fR\^(\|)",

.IR "\fIfopen\fR\^(\|)",

.IR "\fIopen\fR\^(\|)",

.IR "\fIopen_memstream\fR\^(\|)",

.IR "\fIposix_spawn\fR\^(\|)",

.IR "\fIsocket\fR\^(\|)"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "\fB<stdio.h>\fP"

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 7, Copyright (C) 2013 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group.

(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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 .