writes up to
bytes from the buffer pointed
to the file referred to by the file descriptor
The number of bytes written may be less than
if, for example,
there is insufficient space on the underlying physical medium, or the
resource limit is encountered (see
or the call was interrupted by a signal
handler after having written less than
For a seekable file (i.e., one to which
may be applied, for example, a regular file)
writing takes place at the current file offset,
and the file offset is incremented by
the number of bytes actually written.
If the file was
the file offset is first set to the end of the file before writing.
The adjustment of the file offset and the write operation
are performed as an atomic step.
POSIX requires that a
which can be proved to occur after a
has returned returns the new data.
Note that not all file systems are POSIX conforming.
On success, the number of bytes written is returned (zero indicates
nothing was written).
On error, -1 is returned, and errno is set
If count is zero and
refers to a regular file, then
may return a failure status if one of the errors below is detected.
If no errors are detected,
0 will be returned without causing any other effect.
count is zero and
refers to a file other than a regular file,
the results are not specified.
The file descriptor
has been marked non-blocking
and the write would block.
is not a valid file descriptor or is not open for writing.
is outside your accessible address space.
An attempt was made to write a file that exceeds the implementation-defined
maximum file size or the process's file size limit,
or to write at a position past the maximum allowed offset.
The call was interrupted by a signal before any data was written; see
is attached to an object which is unsuitable for writing;
or the file was opened with the
flag, and either the address specified in
the value specified in
or the current file offset is not suitably aligned.
A low-level I/O error occurred while modifying the inode.
The device containing the file referred to by
has no room for the data.
is connected to a pipe or socket whose reading end is closed.
When this happens the writing process will also receive a
(Thus, the write return value is seen only if the program
catches, blocks or ignores this signal.)
Other errors may occur, depending on the object connected to
SVr4, 4.3BSD, POSIX.1-2001.
Under SVr4 a write may be interrupted and return
at any point,
not just before any data is written.
A successful return from
does not make any guarantee that data has been committed to disk.
In fact, on some buggy implementations, it does not even guarantee
that space has successfully been reserved for the data.
The only way to be sure is to call
after you are done writing all your data.
is interrupted by a signal handler before any bytes are written,
then the call fails with the error
if it is interrupted after at least one byte has been written,
the call succeeds, and returns the number of bytes written.