### 7.13 Byte input/output

- `get_byte/2`, `get_byte/1`
- `peek_byte/2`, `peek_byte/1`
- `unget_byte/2`, `unget_byte/1`
- `put_byte/2`, `put_byte/1`

These built-in predicates enable a single byte to be input from and output to a binary stream. `-1` is returned to indicate the end-of-file.

#### 7.13.1 `get_byte/2`, `get_byte/1`

Templates

  `get_byte(+stream_or_alias, ?in_byte)
  get_byte(?in_byte)`

Description

`get_byte(SorA, Byte)` succeeds if `Byte` unifies with the next byte read from the stream associated with the stream-term or alias `SorA`.

`get_byte/1` applies to the current input stream.

Errors

`SorA` is a variable |  | `instantiation_error`
`Byte` is neither a variable nor an in-byte |  | `type_error(in_byte, Byte)`
`SorA` is neither a variable nor a stream-term or alias |  | `domain_error(stream_or_alias, SorA)`
`SorA` is not associated with an open stream |  | `existence_error(stream, SorA)`
`SorA` is an output stream |  | `permission_error(input, stream, SorA)`
`SorA` is associated with a text stream |  | `permission_error(input, text_stream, SorA)`
`SorA` has stream properties `end_of_stream(past)` and `eof_action(error)` |  | `permission_error(input, past_end_of_stream, SorA)`

Portability

ISO predicates.

#### 7.13.2 `peek_byte/2`, `peek_byte/1`

Templates

  `peek_byte(+stream_or_alias, ?in_byte)
  peek_byte(?in_byte)`

Description

`peek_byte(SorA, Byte)` succeeds if `Byte` unifies with the next byte that will be read from the stream associated with the stream-term or alias `SorA`. The byte is not read.

`peek_byte/1` applies to the current input stream.

Errors

`SorA` is a variable |  | `instantiation_error`
`Byte` is neither a variable nor an in-byte |  | `type_error(in_byte, Byte)`
`SorA` is neither a variable nor a stream-term or alias |  | `domain_error(stream_or_alias, SorA)`
`SorA` is not associated with an open stream |  | `existence_error(stream, SorA)`
`SorA` is an output stream |  | `permission_error(input, stream, SorA)`
`SorA` is associated with a text stream |  | `permission_error(input, text_stream, SorA)`
`SorA` has stream properties `end_of_stream(past)` and `eof_action(error)` |  | `permission_error(input, past_end_of_stream, SorA)`

Portability

ISO predicates.

#### 7.13.3 `unget_byte/2`, `unget_byte/1`

Templates

  `unget_byte(+stream_or_alias, +byte)
  unget_byte(+byte)`

Description

`unget_byte(SorA, Byte)` pushes back `Byte` onto the stream associated with the stream-term or alias `SorA`. `Byte` will be the next byte read by `get_byte/2`. The maximum number of bytes that can be successively pushed back is given by the `max_unget` Prolog flag (section 7.22.1).

`unget_byte/1` applies to the current input stream.

Errors

`SorA` is a variable |  | `instantiation_error`
`Byte` is a variable |  | `instantiation_error`
`Byte` is neither a variable nor a byte |  | `type_error(byte, Byte)`
`SorA` is neither a variable nor a stream-term or alias |  | `domain_error(stream_or_alias, SorA)`
`SorA` is not associated with an open stream |  | `existence_error(stream, SorA)`
`SorA` is an output stream |  | `permission_error(input, stream, SorA)`
`SorA` is associated with a text stream |  | `permission_error(input, text_stream, SorA)`

Portability

GNU Prolog predicates.

#### 7.13.4 `put_byte/2`, `put_byte/1`

Templates

  `put_byte(+stream_or_alias, +byte)
  put_byte(+byte)`

Description

`put_byte(SorA, Byte)` writes `Byte` onto the stream associated with the stream-term or alias `SorA`.

`put_byte/1` applies to the current output stream.

Errors

`SorA` is a variable |  | `instantiation_error`
`Byte` is a variable |  | `instantiation_error`
`Byte` is neither a variable nor a byte |  | `type_error(byte, Byte)`
`SorA` is neither a variable nor a stream-term or alias |  | `domain_error(stream_or_alias, SorA)`
`SorA` is not associated with an open stream |  | `existence_error(stream, SorA)`
`SorA` is an output stream |  | `permission_error(output, stream, SorA)`
`SorA` is associated with a text stream |  | `permission_error(output, text_stream, SorA)`

Portability

GNU Prolog predicates.

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