read
OS/161 Reference Manual
Name
read - read data from file
Library
Standard C Library (libc, -lc)
Synopsis
#include <unistd.h>
int
read(int fd, void *buf, size_t buflen);
Description
read reads up to buflen bytes from the file specified by
fd, at the location in the file specified by the current
seek position of the file, and stores them in the space pointed to
by buf. The file must be open for reading.
The current seek position of the file is advanced by the number of
bytes read.
Each read (or write) operation is atomic
relative to other I/O to the same file.
Return Values
The count of bytes read is returned. This count should be
positive. A return value of 0 should be construed as signifying
end-of-file. On error, read returns -1 and sets
errno to a suitable error code for the error
condition encountered.
Note that in some cases, particularly on devices, fewer than
buflen (but greater than zero) bytes may be returned. This
depends on circumstances and does not necessarily signify
end-of-file.
Errors
The following error codes should be returned under the conditions
given. Other error codes may be returned for other errors not
mentioned here.
| | |
| EBADF | fd is not a valid file descriptor, or was
not opened for reading. |
| EFAULT | Part or all of the address space pointed to by
buf is invalid. |
| EIO | A hardware I/O error occurred reading the data. |