fclose - close a stream
int fclose(FILE *stream);
[CX] 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.
[CX] 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.
Upon successful completion, fclose() shall return 0; otherwise, it shall return EOF [CX] and set errno to indicate the error.
The fclose() function shall fail if:
- [CX] The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the write operation.
- [CX] The file descriptor underlying stream is not valid.
- [CX] An attempt was made to write a file that exceeds the maximum file size.
- [XSI] An attempt was made to write a file that exceeds the file size limit of the process.
- [CX] The file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream.
- [CX] The fclose() function was interrupted by a signal.
- [CX] 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.
- [CX] The underlying stream was created by open_memstream() or open_wmemstream() and insufficient memory is available.
- [CX] There was no free space remaining on the device containing the file or in the buffer used by the fmemopen() function.
- [CX] 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:
- [CX] A request was made of a nonexistent device, or the request was outside the capabilities of the device.
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 XBD 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.
Standard I/O Streams, atexit, close, fmemopen, fopen, freopen, getrlimit, open_memstream, ulimit
First released in Issue 1. Derived from Issue 1 of the SVID.
Large File Summit extensions are added.
Extensions beyond the ISO C standard are marked.
The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:
The [EFBIG] error is added as part of the large file support extensions.
The [ENXIO] optional error condition is added.
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''.
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 , XSH/TC1-2008/0114 , and XSH/TC1-2008/0115  are applied.
POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0104  is applied.
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