► |  | The Racket Reference

1 | Language Model
2 | Notation for Documentation
3 | Syntactic Forms
4 | Datatypes
5 | Structures
6 | Classes and Objects
7 | Units
8 | Contracts
9 | Pattern Matching
10 | Control Flow
11 | Concurrency and Parallelism
12 | Macros
13 | Input and Output
14 | Reflection and Security
15 | Operating System
16 | Memory Management
17 | Unsafe Operations
18 | Running Racket
| Bibliography
| Index

► | 13 | Input and Output

13.1 | Ports
13.2 | Byte and String Input
13.3 | Byte and String Output
13.4 | Reading
13.5 | Writing
13.6 | Pretty Printing
13.7 | Reader Extension
13.8 | Printer Extension
13.9 | Serialization
13.10 | Fast-Load Serialization

▼ | 13.1 | Ports

13.1.1 | Encodings and Locales
13.1.2 | Managing Ports
13.1.3 | Port Buffers and Positions
13.1.4 | Counting Positions, Lines, and Columns
13.1.5 | File Ports
13.1.6 | String Ports
13.1.7 | Pipes
13.1.8 | Structures as Ports
13.1.9 | Custom Ports
13.1.10 | More Port Constructors, Procedures, and Events

On this page:

input-port?
output-port?
port?
close-input-port
close-output-port
port-closed?
port-closed-evt
current-input-port
current-output-port
current-error-port
file-stream-port?
terminal-port?
eof
eof-object?

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##### 13.1.2`` Managing Ports

> procedure (input-port? v) → boolean?
> v : any/c

Returns #t if v is an input port, #f otherwise.

> procedure (output-port? v) → boolean?
> v : any/c

Returns #t if v is an output port, #f otherwise.

> procedure (port? v) → boolean?
> v : any/c

Returns #t if either (input-port? v) or (output-port? v) is #t, #f otherwise.

> procedure (close-input-port in) → void?
> in : input-port?

Closes the input port in. For some kinds of ports, closing the port releases lower-level resources, such as a file handle. If the port is already closed, close-input-port has no effect.

> procedure (close-output-port out) → void?
> out : output-port?

Closes the output port out. For some kinds of ports, closing the port releases lower-level resources, such as a file handle. Also, if the port is buffered, closing may first flush the port before closing it, and this flushing process can block. If the port is already closed, close-output-port has no effect.

> procedure (port-closed? port) → boolean?
> port : port?

Returns #t if the input or output port port is closed, #f otherwise.

> procedure (port-closed-evt port) → evt?
> port : port?

Return a synchronizable event that becomes ready for synchronization when port is closed. The synchronization result of a port-closed event is the port-closed event itself.

> parameter (current-input-port) → input-port?
> (current-input-port in) → void?
> in : input-port?

A parameter that determines a default input port for many operations, such as read.

> parameter (current-output-port) → output-port?
> (current-output-port out) → void?
> out : output-port?

A parameter that determines a default output port for many operations, such as write.

> parameter (current-error-port) → output-port?
> (current-error-port out) → void?
> out : output-port?

A parameter that determines an output port that is typically used for errors and logging. For example, the default error display handler writes to this port.

> procedure (file-stream-port? port) → boolean?
> port : port?

Returns #t if the given port is a file-stream port (see File Ports), #f otherwise.

> procedure (terminal-port? port) → boolean?
> port : port?

Returns #t if the given port is attached to an interactive terminal, #f otherwise.

> value eof : eof-object?

A value (distinct from all other values) that represents an end-of-file.

> procedure (eof-object? a) → boolean?
> a : any/c

Returns #t if v is eof, #f otherwise.
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