ftruncate
Synopsis
#include <unistd.h>
int ftruncate(int fildes, off_t length);
Status
Partially implemented
Conformance
IEEE Std 1003.1-2017
Description
The purpose is to truncate a file to a specified length. If fildes is not a valid file descriptor open for writing,
the ftruncate() function shall fail.
If fildes refers to a regular file, the ftruncate() function shall cause the size of the file to be truncated to
length.
If the size of the file previously exceeded length, the extra data shall no longer be available to reads on the file.
If the file previously was smaller than this size, ftruncate() shall increase the size of the file. If the file size
is increased, the extended area shall appear as if it were zero-filled. The value of the seek pointer shall not be
modified by a call to ftruncate().
Upon successful completion, if fildes refers to a regular file, ftruncate() shall mark for update the last data
modification and last file status change timestamps of the file and the S_ISUID and S_ISGID bits of the file mode
may be cleared.
If the ftruncate() function is unsuccessful, the file is unaffected.
If the request caused the file size to exceed the soft file size limit for the process, the request shall fail, and
the implementation shall generate the SIGXFSZ signal for the thread.
If fildes refers to a directory, ftruncate() shall fail.
If fildes refers to any other file type, except a shared memory object, the result is unspecified.
If fildes refers to a shared memory object, ftruncate() shall set the size of the shared memory object to length.
If the effect of ftruncate() is to decrease the size of a memory mapped file or a shared memory object and whole pages
beyond the new end were previously mapped, then the whole pages beyond the new end shall be discarded.
References to discarded pages shall result in the generation of a SIGBUS signal.
If the effect of ftruncate() is to increase the size of a memory object, it is unspecified whether the
contents of any mapped pages between the old end-of-file and the new are flushed to the underlying object.
Return value
Upon successful completion, ftruncate() shall return 0, otherwise, -1 shall be returned and errno
set to indicate the error.
Errors
The ftruncate() function shall fail if:
EINTR- A signal was caught during execution.EINVAL- The length argument was less than0.EFBIGorEINVAL- The length argument was greater than the maximum file size.EFBIG- The file is a regular file and length is greater than the offset maximum established in the open file description associated with fildes.EIO- An I/O error occurred while reading from or writing to a file system.EBADForEINVAL- The fildes argument is not a file descriptor open for writing.
Tests
Untested
Known bugs
None