FDOPEN(3)                  POSIX Programmer's Manual                 FDOPEN(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 .



IEEE/The Open Group                  2017                            FDOPEN(3)
