read.2 (2010 09)

r
read(2) read(2)
Upon successful completion, readv() marks for update the st_atime field of the file.
The
pread() function performs the same action as
read(), except that it reads from a given position
in the file without changing the file pointer. The first three arguments of
pread() are the same as
read() with the addition of a fourth argument
offset for the desired position inside the file. An
attempt to perform a
pread() on a file that is incapable of seeking results in an error.
RETURN VALUE
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 (2) and termio (7)), or
• The number of bytes left in the file is less than nbyte bytes.
•
read() was interrupted by a signal after it had successfully read some, but not all of the data
requested.
When an end-of-file is reached, a value of 0 is returned. Otherwise, a −1 is returned and
errno is set to
indicate the error.
Upon successful completion,
pread() and readv() return a non-negative integer indicating the
number of bytes actually read. Otherwise, the functions return −1 and set
errno to indicate the error.
ERRORS
The
read(), pread() and readv() functions will fail if:
[EAGAIN] Enforcement-mode file and record locking is set,
O_NDELAY or O_NONBLOCK
is set, and there is a blocking write lock.
[EBADF] The fildes argument is not a valid file descriptor open for reading.
[EBADMSG] The file is a
STREAM file that is set to control-normal mode and the message
waiting to be read includes a control part.
[EDEADLK] A resource deadlock would occur as a result of this operation (see lockf (2) and
fcntl (2)).
[EFAULT] buf points outside the allocated address space. Reliable detection of this error is
implementation dependent.
[EINTR] A signal was caught before any data was transferred (see signal (5)).
[EINVAL] The starting file offset associated with fildes is greater than the maximum sup-
ported file size.
[EINVAL] The
STREAM or multiplexer referenced by fildes is linked (directly or indirectly)
downstream from a multiplexer.
[EIO] A physical I/O error has occurred.
[EIO] The process is a member of a background process attempting to read from its
controlling terminal, the process is ignoring or blocking the
SIGTTIN signal or
the process group is orphaned. This error may also be generated for
implementation-dependent reasons.
[EISDIR] The fildes argument refers to a directory and the implementation does not allow
the directory to be read using
read(), pread() or readv(). The read-
dir() function should be used instead.
[ENOLCK] The system record lock table is full, preventing the read from sleeping until the
blocking write lock is removed.
The
readv() function will fail if:
[EINVAL] The sum of the iov_len values in the iov array overflowed an ssize_t .
[EFAULT] iov_base or iov points outside of the allocated address space. The reliable detec-
tion of this error is implementation-dependent.
The
read(), pread() and readv() functions may fail if:
[ENXIO] A request was made of a non-existent device, or the request was outside the
capabilities of the device.
HP-UX 11i Version 3: September 2010 − 3 − Hewlett-Packard Company 3