FDOPEN(3C) Standard C Library Functions FDOPEN(3C)

NAME

fdopen - associate a stream with a file descriptor

SYNOPSIS

#include <stdio.h>

FILE *fdopen(int fildes, const char *mode);

DESCRIPTION

The fdopen() function associates a stream with a file descriptor fildes.


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


r or rb Open a file for reading.
w or wb Open a file for writing.
a or ab Open a file for writing at end of file.
r+, rb+ or r+b Open a file for update (reading and
writing).
w+, wb+ or w+b Open a file for update (reading and
writing).
a+, ab+ or a+b Open a file for update (reading and
writing) at end of file.


The meaning of these flags is exactly as specified for the fopen(3C)
function, except that modes beginning with w do not cause truncation of
the file. A trailing F character can also be included in the mode
argument as described in fopen(3C) to enable extended FILE facility.


The mode of the stream must be allowed by the file access mode of the
open file. The file position indicator associated with the new stream is
set to the position indicated by the file offset associated with the file
descriptor.


The fdopen() function preserves the offset maximum previously set for the
open file description corresponding to fildes.


The error and end-of-file indicators for the stream are cleared. The
fdopen() function may cause the st_atime field of the underlying file to
be marked for update.


If fildes refers to a shared memory object, the result of the fdopen()
function is unspecified.

RETURN VALUES

Upon successful completion, fdopen() returns a pointer to a stream.
Otherwise, a null pointer is returned and errno is set to indicate the
error.


The fdopen() function may fail and not set errno if there are no free
stdio streams.

ERRORS

The fdopen() function may fail if:

EBADF
The fildes argument is not a valid file descriptor.


EINVAL
The mode argument is not a valid mode.


EMFILE
{FOPEN_MAX} streams are currently open in the calling process.

{STREAM_MAX} streams are currently open in the calling process.


ENOMEM
There is insufficient space to allocate a buffer.

USAGE

A process is allowed to have at least {FOPEN_MAX} stdio streams open at a
time. For 32-bit applications, however, the underlying ABIs formerly
required that no file descriptor used to access the file underlying a
stdio stream have a value greater than 255. To maintain binary
compatibility with earlier Solaris releases, this limit still constrains
32-bit applications.


File descriptors are obtained from calls like open(2), dup(2), creat(2)
or pipe(2), which open files but do not return streams. Streams are
necessary input for almost all of the standard I/O library functions.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | See below. |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+


The F character in the mode argument is Evolving. In all other respects
this function is Standard.

SEE ALSO

creat(2), dup(2), open(2), pipe(2), fclose(3C), fopen(3C), attributes(7),
standards(7)

April 18, 2006 FDOPEN(3C)