Man Linux: Main Page and Category List

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 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.

       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 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.

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(), 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.

FUTURE DIRECTIONS

       None.

SEE ALSO

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

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 .