read.2 (2010 09)

read(2) read(2)

The readv() function may fail if:

[EINVAL] The

iovcnt argument was less than or equal to 0, or greater than

{IOV_MAX}.

The

pread() function will fail and the ﬁle pointer remains unchanged if:

[EINVAL] The offset argument is invalid. The value is negative.

[EOVERFLOW] The ﬁle is a regular ﬁle and an attempt was made to read at or beyond the offset

maximum associated with the ﬁle.

[ESPIPE] ﬁldes is associated with a pipe or FIFO.

EXAMPLES

Assuming a process opened a ﬁle for reading, the following call to read (2) reads

BUFSIZ bytes from the

ﬁle into the buffer pointed to by mybuf:

#include <stdio.h> /* include this for BUFSIZ definition */

char mybuf[BUFSIZ];

int nbytes, fildes;

nbytes = read (fildes, mybuf, BUFSIZ);

WARNINGS

Record locking might not be enforced by the system, depending on the setting of the ﬁle’s mode bits (see

lockf (2)).

Character-special devices, and raw disks in particular, apply constraints on how

read() can be used.

See the speciﬁc Section (7) entries for details on particular devices.

In general, avoid using

read() to get the contents of a directory; use the readdir() library routine

(see directory (3C)).

DEPENDENCIES

NFS

When obtaining the contents of a directory on an NFS ﬁle system, the

readdir() library routine must

be used (see directory (3C)). read() returns with an error if used to read a directory using NFS.

AUTHOR

read() was developed by HP, AT&T, and the University of California, Berkeley.