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.

NAME

       fdopen — associate a stream with a file descriptor

SYNOPSIS

       #include <stdio.h>

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

DESCRIPTION

       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
       indicated by the file offset associated with the file descriptor.

       The  error  and  end-of-file  indicators  for  the  stream shall be cleared.  The fdopen()
       function may cause the last data access timestamp 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.

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

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

RETURN VALUE

       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.

ERRORS

       The fdopen() function shall fail if:

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

       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.

       ENOMEM Insufficient space to allocate a buffer.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

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

RATIONALE

       The file descriptor may have been obtained from open(), creat(), pipe(),  dup(),  fcntl(),
       or  socket();  inherited  through  fork(),  posix_spawn(), or exec; or perhaps obtained by
       other means.

       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 POSIX.1‐2017, a good implementation of append  (a)  mode  would
       cause the O_APPEND flag to be set.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section  2.5.1,  Interaction  of  File  Descriptors  and  Standard  I/O Streams, fclose(),
       fmemopen(), fopen(), open(), open_memstream(), posix_spawn(), socket()

       The Base Definitions volume of POSIX.1‐2017, <stdio.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1-2017,  Standard  for  Information Technology -- Portable Operating System Interface
       (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C)  2018  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 .

       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 .