# Method Stdio.Fd()->read()

Method read

  `string read()`
  `string read(int len)`
  `string read(int len, bool not_all)`

Description

  Read data from a file or a stream.

  Attempts to read len bytes from the file, and return it as a string. Less than len bytes can be returned if:

  - end-of-file is encountered for a normal file, or

  - it's a stream that has been closed from the other end, or

  - it's a stream in nonblocking mode, or

  - it's a stream and not_all is set, or

  - not_all isn't set and an error occurred (see below).

  If not_all is nonzero, read() does not try its best to read as many bytes as you have asked for, but merely returns as much as the system read function returns. This is mainly useful with stream devices which can return exactly one row or packet at a time. If not_all is used in blocking mode, read() only blocks if there's no data at all available.

  If something goes wrong and not_all is set, zero is returned. If something goes wrong and not_all is zero or left out, then either zero or a string shorter than len is returned. If the problem persists then a later call to read() fails and returns zero, however.

  If everything went fine, a call to errno() directly afterwards returns zero. That includes an end due to end-of-file or remote close.

  If no arguments are given, read() reads to the end of the file or stream.

  If any file descriptors have been sent by the other side of the stream, receive_fd() will be called once for every sent file descriptor.

Note

  It's not necessary to set not_all to avoid blocking reading when nonblocking mode is used.

Note

  When at the end of a file or stream, repeated calls to read() will return the empty string since it's not considered an error. The empty string is never returned in other cases, unless nonblocking mode is used or len is zero.

See also

  read_oob(), write(), receive_fd(), send_fd()