Copyright (c) 1980 Regents of the University of California.
All rights reserved. The Berkeley software License Agreement
specifies the terms and conditions for redistribution.

@(#)read.2 6.1 (Berkeley) 05/09/85

C 4 read, readv - read input

cc = read(d, buf, nbytes)
int cc, d;
char *buf;
int 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 iovec array: iov[0], iov[1], ..., iov[iovcnt\|-\|1].

For readv , the iovec structure is defined as

struct iovec {
 caddr_t iov_base;
 int 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 next.

On objects capable of seeking, the read starts at a position given by the pointer associated with d , see lseek (2). Upon return from read , the pointer is incremented by the number 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 a 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 file which has that many bytes left before the end-of-file, but in no other cases.

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:

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

15 [EFAULT] Buf points outside the allocated address space.

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

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

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

15 [EINVAL] One of the iov_len values in the iov array was negative.

15 [EINVAL] The sum of the iov_len values in the iov array overflowed a 32-bit integer.

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