READ(2)
NAME
read, readv − read input
USAGE
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;
DESCRIPTION
Read attempts to read nbytes of data from the object specified 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_tiov_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 completely fill an area before proceeding to the next.
On objects that permit seeking, the read starts at a position given by the pointer associated with d; see lseek(2). Upon return from read, the pointer increments by the number of bytes actually read.
Objects that do not permit 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 only if the descriptor refers to a file in which that many bytes remain before the end-of-file.
If the returned value is zero, then the call reached an end-of-file.
RETURN VALUE
A successful call returns the number of bytes actually read. A failed call returns -1 and sets errno as indicated below.
ERRORS
Read and readv will fail if one or more of the following are true:
[EBADF] D is not a valid file descriptor open for reading.
[EFAULT] Buf points outside the allocated address space.
[EINTR] A read from a slow device was interrupted before any data arrived by the delivery of a signal.
[EWOULDBLOCK]
The file descriptor is marked as non-blocking, and a read would block.
In addition, readv may return one of the following errors:
[EINVAL] Iovcnt was less than or equal to zero or greater than 16.
[EINVAL] One of the iov_len values in the iov array was negative.
[EINVAL] The sum of the iov_len values in the iov array overflowed a 32-bit integer.