The functionality described on this reference page is aligned with
the ISO C standard. Any conflict between the
requirements described here and the ISO C standard is unintentional.
This volume of IEEE Std 1003.1-2001 defers to
the ISO C standard.
The fclose() function shall cause the stream pointed to by stream
to be flushed and the associated file to be
closed. Any unwritten buffered data for the stream shall be written
to the file; any unread buffered data shall be discarded.
Whether or not the call succeeds, the stream shall be disassociated
from the file and any buffer set by the setbuf() or setvbuf()
function shall be
disassociated from the stream. If the associated buffer was automatically
allocated, it shall be deallocated.
fclose() function shall mark for update the st_ctime and
st_mtime fields of the underlying file, if the stream
was writable, and if buffered data remains that has not yet been written
to the file. The fclose() function shall perform
the equivalent of a close() on the file descriptor that is associated
with the stream
pointed to by stream.
After the call to fclose(), any use of stream results
in undefined behavior.
Upon successful completion, fclose() shall return 0; otherwise,
it shall return EOF and set
errno to indicate the error.
The fclose() function shall fail if:
The O_NONBLOCK flag is set for the file descriptor underlying stream
and the process would be delayed in the write
The file descriptor underlying stream is not valid.
attempt was made to write a file that exceeds the maximum file size.
An attempt was made to write a file that exceeds the process' file
The file is a regular file and an attempt was made to write at or
beyond the offset maximum associated with the corresponding
The fclose() function was interrupted by a signal.
The process is a member of a background process group attempting to
write to its controlling terminal, TOSTOP is set, the process
is neither ignoring nor blocking SIGTTOU, and the process group of
the process is orphaned. This error may also be returned under
There was no free space remaining on the device containing the file.
attempt is made to write to a pipe or FIFO that is not open for reading
by any process. A SIGPIPE signal shall also be sent to the
The fclose() function may fail if:
request was made of a nonexistent device, or the request was outside
the capabilities of the device.
The following sections are informative.
close() , fopen() , getrlimit() , ulimit()
, 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 original Standard can be obtained online at