The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group


fclose - close a stream


#include <stdio.h>

int fclose(FILE *


[CX] [Option Start] 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 POSIX.1-2008 defers to the ISO C standard. [Option End]

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.

[CX] [Option Start] If the file is not already at EOF, and the file is one capable of seeking, the file offset of the underlying open file description shall be set to the file position of the stream if the stream is the active handle to the underlying file description.

The fclose() function shall mark for update the last data modification and last file status change timestamps 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. [Option End]

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 [CX] [Option Start]  and set errno to indicate the error. [Option End]


The fclose() function shall fail if:

[CX] [Option Start] The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the write operation. [Option End]
[CX] [Option Start] The file descriptor underlying stream is not valid. [Option End]
[CX] [Option Start] An attempt was made to write a file that exceeds the maximum file size. [Option End]
[XSI] [Option Start] An attempt was made to write a file that exceeds the file size limit of the process. [Option End]
[CX] [Option Start] The file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream. [Option End]
[CX] [Option Start] The fclose() function was interrupted by a signal. [Option End]
[CX] [Option Start] The process is a member of a background process group attempting to write to its controlling terminal, TOSTOP is set, the calling thread is not blocking SIGTTOU, the process is not ignoring SIGTTOU, and the process group of the process is orphaned. This error may also be returned under implementation-defined conditions. [Option End]
[CX] [Option Start] The underlying stream was created by open_memstream() or open_wmemstream() and insufficient memory is available. [Option End]
[CX] [Option Start] There was no free space remaining on the device containing the file or in the buffer used by the fmemopen() function. [Option End]
[CX] [Option Start] An 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 thread. [Option End]

The fclose() function may fail if:

[CX] [Option Start] A request was made of a nonexistent device, or the request was outside the capabilities of the device. [Option End]

The following sections are informative.










Standard I/O Streams, close, fmemopen, fopen, getrlimit, open_memstream, ulimit

XBD <stdio.h>


First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 5

Large File Summit extensions are added.

Issue 6

Extensions beyond the ISO C standard are marked.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

The DESCRIPTION is updated to note that the stream and any buffer are disassociated whether or not the call succeeds. This is for alignment with the ISO/IEC 9899:1999 standard.

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/28 is applied, updating the [EAGAIN] error in the ERRORS section from ``the process would be delayed'' to ``the thread would be delayed''.

Issue 7

Austin Group Interpretation 1003.1-2001 #002 is applied, clarifying the interaction of file descriptors and streams.

The [ENOSPC] error condition is updated and the [ENOMEM] error is added from The Open Group Technical Standard, 2006, Extended API Set Part 1.

Changes are made related to support for finegrained timestamps.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0113 [87], XSH/TC1-2008/0114 [79], and XSH/TC1-2008/0115 [14] are applied.

End of informative text.


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