READ(S) XENIX System V READ(S)
Name
read - Reads from a file.
Syntax
int read (fildes, buf, nbyte)
int fildes;
char *buf;
unsigned nbyte;
Description
fildes is a file descriptor obtained from a creat, open,
dup, fcntl, or pipe system call.
read attempts to read nbyte bytes from the file associated
with fildes into the buffer pointed to by buf.
On devices capable of seeking, the read starts at a position
in the file given by the file pointer associated with
fildes. Upon return from read, the file pointer is
incremented by the number of bytes actually read.
Devices that are incapable of seeking always read from the
current position. The value of a file pointer associated
with such a file is undefined.
Upon successful completion, read returns the number of bytes
actually read and placed in the buffer; this number may be
less than nbyte if the file is associated with a
communication line (see ioctl(S) and tty(M)), or if the
number of bytes left in the file is less than nbyte bytes.
A value of 0 is returned when an end-of-file has been
reached.
When attempting to read from an empty pipe (or FIFO):
If O_NDELAY is set, the read will return a 0.
If O_NDELAY is clear, the read will block until data is
written to the file or the file is no longer open for
writing.
When attempting to read a file associated with a character
special file that has no data currently available:
If O_NDELAY is set, the read will return a 0.
If O_NDELAY is clear, the read will block until data
becomes available.
read will fail if one or more of the following are true:
fildes is not a valid file descriptor open for reading.
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READ(S) XENIX System V READ(S)
[EBADF]
buf points outside the allocated address space.
[EFAULT]
A signal was caught during the read system call.
[EINTR]
Return Value
Upon successful completion a nonnegative integer is returned
indicating the number of bytes actually read. Otherwise, -1
is returned and errno is set to indicate the error.
See Also
creat(S), dup(S), fcntl(S), ioctl(S), open(S), pipe(S),
rdchk(S), tty(M)
Notes
Reading a region of a file locked with locking causes read
to hang indefinitely until the locked region is unlocked.
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