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Linux 2.6 - man page for fdopen (linux section 3posix)

FDOPEN(P)			    POSIX Programmer's Manual				FDOPEN(P)

       fdopen - associate a stream with a file descriptor

       #include <stdio.h>

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

       The fdopen() function shall associate a stream with a file descriptor.

       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+ or rb+ or r+b
	      Open a file for update (reading and writing).

       w+ or wb+ or w+b
	      Open a file for update (reading and writing).

       a+ or 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 in fopen(), except that modes beginning
       with w shall not cause truncation of the file.

       Additional values for the mode argument may be supported by an implementation.

       The application shall ensure that the mode of the stream as expressed by the mode argument
       is  allowed  by	the file access mode of the open file description to which fildes refers.
       The file position indicator associated with the new stream is set to  the  position  indi-
       cated by the file offset associated with the file descriptor.

       The  error and end-of-file indicators for the stream shall be cleared.  The fdopen() func-
       tion 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 unspec-

       If fildes refers to a typed memory object, the result of the fdopen() function is unspeci-

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

       Upon successful completion, fdopen() shall return a pointer to a stream; otherwise, a null
       pointer shall be returned and errno set to indicate the error.

       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.

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

       ENOMEM Insufficient space to allocate a buffer.

       The following sections are informative.


       File descriptors are obtained from calls like open(), dup(),  creat(),  or  pipe(),  which
       open files but do not return streams.

       The  file  descriptor  may  have  been  obtained  from  open(), creat(), pipe(), dup(), or
       fcntl(); inherited through fork() or exec; or perhaps obtained  by  implementation-defined
       means, such as the 4.3 BSD socket() call.

       The  meanings  of  the mode arguments of fdopen() and fopen() differ.  With fdopen(), open
       for write (w or w+) does not truncate, and append (a or a+) cannot create for writing. The
       mode argument formats that include a b are allowed for consistency with the ISO C standard
       function fopen(). The b 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 (a) mode
       would cause the O_APPEND flag to be set.


       Interaction of File Descriptors and Standard I/O Streams , fclose() , fopen() ,	open()	,
       the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					FDOPEN(P)

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