RTEMS 4.5.0 On-Line Library

Input and Output Primitives Manager read - Reads from a file.

RTEMS POSIX API User's Guide

#include <unistd.h>

int read(
  int           fildes,
  void         *buf,
  unsigned int  nbyte
);

On error, this routine returns -1 and sets errno to one of the following:

EAGAIN: The O_NONBLOCK flag is set for a file descriptor and the process would be delayed in the I/O operation.
EBADF: Invalid file descriptor
EINTR: Function was interrupted by a signal.
EIO: Input or output error

The read() function reads nbyte bytes from the file associated with fildes into the buffer pointed to by buf.

The read() function returns the number of bytes actually read and placed in the buffer. This will be less than nbyte if:

The number of bytes left in the file is less than nbyte.
The read() request was interrupted by a signal.
The file is a pipe or FIFO or special file with less than nbytes immediately available for reading.

When attempting to read from any empty pipe or FIFO:

If no process has the pipe open for writing, zero is returned to indicate end-of-file.
If some process has the pipe open for writing and O_NONBLOCK is set, -1 is returned and errno is set to EAGAIN.
If some process has the pipe open for writing and O_NONBLOCK is clear, read() waits for some data to be written or the pipe to be closed.

When attempting to read from a file other than a pipe or FIFO and no data is available.

NONE

RTEMS POSIX API User's Guide