Character input/output

6.12

Character input/output

These built-in predicates enable a single character or character code to be input from and output to a text stream. The atom end_of_file is returned as character to indicate the end-of-file. -1 is returned as character code to indicate the end-of-file.

6.12.1 get_char/2, get_char/1, get_code/1, get_code/2

Templates

: get_char(+stream_or_alias, ?in_character) get_char(?in_character) get_code(+stream_or_alias, ?in_character_code) get_code(?in_character_code)

Description

get_char(SorA, Char) succeeds if Char unifies with the next character read from the stream associated with the stream-term or alias SorA.

get_code/2 is similar to get_char/2 but deals with character codes.

get_char/1 and get_code/1 apply to the current input stream.

Errors

SorA is a variable instantiation_error

Char is neither a variable nor an in-character type_error(in_character, Char)

Code is neither a variable nor an integer type_error(integer, Code)

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 binary stream permission_error(input, binary_stream, SorA)

SorA has stream properties end_of_stream(past) and eof_action(error) permission_error(input, past_end_of_stream, SorA)

The entity input from the stream is not a character representation_error(character)

Code is an integer but not an in-character code representation_error(in_character_code)

Portability

ISO predicates.

6.12.2 get_code_no_echo/2, get_code_no_echo/1

Templates

: get_code_no_echo(+stream_or_alias, ?integer) get_code_no_echo(?integer)

Description

get_code_no_echo/2 is similar to get_code/2 (section 6.12.1) except that if the associated source is a terminal the input is not echoed. This is possible only if the linedit facility has been installed (section 2.2.5) otherwise get_code_no_echo/2 is similar to get_code/2. Any integer can be returned (not only an in-character code) to allow for function key reading.

get_code_no_echo/1 applies to the current input stream.

Errors

SorA is a variable instantiation_error

Code is neither a variable nor an integer type_error(integer, Code)

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 binary stream permission_error(input, binary_stream, SorA)

SorA has stream properties end_of_stream(past) and eof_action(error) permission_error(input, past_end_of_stream, SorA)

Portability

GNU Prolog predicates.

6.12.3 peek_char/2, peek_char/1, peek_code/1, peek_code/2

Templates

: peek_char(+stream_or_alias, ?in_character) peek_char(?in_character) peek_code(+stream_or_alias, ?in_character_code) peek_code(?in_character_code)

Description

peek_char(SorA, Char) succeeds if Char unifies with the next character that will be read from the stream associated with the stream-term or alias SorA. The character is not read.

peek_code/2 is similar to peek_char/2 but deals with character codes.

peek_char/1 and peek_code/1 apply to the current input stream.

Errors