fclose - Man Page

close a stream


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.


#include <stdio.h>

int fclose(FILE *stream);


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.1-2017 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.

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.

After the call to fclose(), any use of stream results in undefined behavior.

Return Value

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 thread would be delayed in the write operation.


The file descriptor underlying stream is not valid.


An attempt was made to write a file that exceeds the maximum file size.


An attempt was made to write a file that exceeds the file size limit of the process.


The file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream.


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 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.


The underlying stream was created by open_memstream() or open_wmemstream() and insufficient memory is available.


There was no free space remaining on the device containing the file or in the buffer used by the fmemopen() function.


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.

The fclose() function may fail if:


A request was made of a nonexistent device, or the request was outside the capabilities of the device.

The following sections are informative.



Application Usage

Since after the call to fclose() any use of stream results in undefined behavior, fclose() should not be used on stdin, stdout, or stderr except immediately before process termination (see the Base Definitions volume of POSIX.1-2017, Section 3.303, Process Termination), so as to avoid triggering undefined behavior in other standard interfaces that rely on these streams. If there are any atexit() handlers registered by the application, such a call to fclose() should not occur until the last handler is finishing. Once fclose() has been used to close stdin, stdout, or stderr, there is no standard way to reopen any of these streams.

Use of freopen() to change stdin, stdout, or stderr instead of closing them avoids the danger of a file unexpectedly being opened as one of the special file descriptors STDIN_FILENO, STDOUT_FILENO, or STDERR_FILENO at a later time in the application.



Future Directions


See Also

Section 2.5, Standard I/O Streams, atexit(), close(), fmemopen(), fopen(), freopen(), getrlimit(), open_memstream(), ulimit()

The Base Definitions volume of POSIX.1-2017, <stdio.h>

Referenced By

close(3p), fdopen(3p), fopen(3p), freopen(3p), open_memstream(3p), stdin(3p), stdio.h(0p).

2017 IEEE/The Open Group POSIX Programmer's Manual