WRITE(2)

NAME
write - write to a file descriptor

SYNOPSIS
#include <unistd.h>

ssize_t write(int fd, const void *buf, size_t count);

DESCRIPTION
write() writes up to count bytes to the file referenced by the file descriptor fd from the buffer starting at buf. POSIX requires that a read(2) which can be proved to occur after a write() has returned returns the new data. Note that not all file systems are POSIX conforming.

RETURN VALUE
On success, the number of bytes written are returned (zero indicates nothing was written). On error, -1 is returned, and errno is set appropriately. If count is zero and fd refers to a regular file, then write () 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. If count is zero and fd refers to a file other than a regular file, the results are not specified.

ERRORS

EAGAIN
    Non-blocking I/O has been selected using O_NONBLOCK and the write would block.

EBADF
    fd is not a valid file descriptor or is not open for writing.

EFAULT
    buf is outside your accessible address space.

EFBIG
    An attempt was made to write a file that exceeds the implementation-defined maximum file size or the process' file size limit, or to write at a position past the maximum allowed offset.

EINTR
    The call was interrupted by a signal before any data was written.

EINVAL
    fd is attached to an object which is unsuitable for writing; or the file was opened with the O_DIRECT flag, and either the address specified in buf, the value specified in count, or the current file offset is not suitably aligned.

EIO A low-level I/O error occurred while modifying the inode.

ENOSPC
    The device containing the file referred to by fd has no room for the data.

EPIPE
    fd is connected to a pipe or socket whose reading end is closed. When this happens the writing process will also receive a SIGPIPE signal. (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 fd.

CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001. Under SVr4 a write may be interrupted and return EINTR at any point, not just before any data is written.

NOTES
A successful return from write() 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 fsync(2) after you are done writing all your data.

SEE ALSO
close(2), fcntl(2), fsync(2), ioctl(2), lseek(2), open(2), pwrite(2), read(2), select(2), writev(2), fwrite(3)