fdopen(3p) — Linux manual page


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

PROLOG         top

       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         top

       fdopen — associate a stream with a file descriptor

SYNOPSIS         top

       #include <stdio.h>

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

DESCRIPTION         top

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

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

       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-

       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

       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         top

       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         top

       The fdopen() function shall fail if:

       EMFILE {STREAM_MAX} streams are currently open in the calling

       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         top



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

RATIONALE         top

       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.1‐2008, a
       good implementation of append (a) mode would cause the O_APPEND flag
       to be set.



SEE ALSO         top

       Section 2.5.1, Interaction of File Descriptors and Standard I/O
       Streams, fclose(3p), fmemopen(3p), fopen(3p), open(3p),
       open_memstream(3p), posix_spawn(3p), socket(3p)

       The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                          FDOPEN(3P)

Pages that refer to this page: stdio.h(0p)fileno(3p)fmemopen(3p)fopen(3p)freopen(3p)open_memstream(3p)open_wmemstream(3p)