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BSD 2.11 - man page for read (bsd section 2)

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READ(2) 										  READ(2)

       read, readv - read input

       cc = read(d, buf, nbytes)
       int cc, d;
       char *buf;
       unsigned short nbytes;

       #include <sys/types.h>
       #include <sys/uio.h>

       cc = readv(d, iov, iovcnt)
       int cc, d;
       struct iovec *iov;
       int iovcnt;

       Read  attempts  to read nbytes of data from the object referenced by the descriptor d into
       the buffer pointed to by buf.  Readv performs the same action, but scatters the input data
       into  the  iovcnt  buffers specified by the members of the iov array: iov[0], iov[1], ...,

       For readv, the iovec structure is defined as

	      struct iovec {
		   caddr_t   iov_base;
		   u_short   iov_len;

       Each iovec entry specifies the base address and length of an area  in  memory  where  data
       should  be  placed.   Readv  will  always fill an area completely before proceeding to the

       On objects capable of seeking, the read starts at a position given by the pointer  associ-
       ated with d (see lseek(2)).  Upon return from read, the pointer is incremented by the num-
       ber of bytes actually read.

       Objects that are not capable of seeking always read from the current position.  The  value
       of the pointer associated with such an object is undefined.

       Upon  successful  completion,  read and readv return the number of bytes actually read and
       placed in the buffer.  The system guarantees to read the number of bytes requested if  the
       descriptor  references a normal file that has that many bytes left before the end-of-file,
       but in no other case.

       If the returned value is 0, then end-of-file has been reached.

       If successful, the number of bytes actually read is returned.  Otherwise, a -1 is returned
       and the global variable errno is set to indicate the error.

       Read and readv will fail if one or more of the following are true:

       [EBADF]	      D is not a valid file or socket descriptor open for reading.

       [EFAULT]       Buf points outside the allocated address space.

       [EIO]	      An I/O error occurred while reading from the file system.

       [EINTR]	      A  read  from  a slow device was interrupted before any data arrived by the
		      delivery of a signal.

       [EINVAL]       The pointer associated with d was negative.

       [EWOULDBLOCK]  The file was marked for non-blocking I/O, and no	data  were  ready  to  be

       In addition, readv may return one of the following errors:

       [EINVAL]       Iovcnt was less than or equal to 0, or greater than 16.

       [EINVAL]       The sum of the iov_len values in the iov array overflowed a short.

       [EFAULT]       Part of the iov points outside the process's allocated address space.

       dup(2), fcntl(2), open(2), pipe(2), select(2), socket(2), socketpair(2)

4th Berkeley Distribution		  August 1, 1987				  READ(2)
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