Assigns an I/O channel
to a terminal
| Language element: |
function
|
| Category: |
terminal-access
|
| OpenVMS specifics: |
All aspects are
host-specific
|
|
TTOPEN(control-specification,channel)
|
- control-specification
- is the control string that specifies the
terminal and processing options, separated from each other by blanks. It can
be a character variable, a character literal enclosed in double quotation
marks, or another character expression. The value for control-specification gives the device name and processing options and has the following
form:
|
DEVICE=name <processing-option-list>
|
Each
argument can be abbreviated to the shortest unique
spelling. There is no default.
- name
- specifies the terminal name for subsequent I/O operations.
DEVICE=name is
required.
- processing-option-list
- can be one or more of the following, separated
by blanks:
-
BUFFERFULL | NOBUFFERFULL
- If you specify BUFFERFULL as one of the
processing options when you enumerate the control string for the TTOPEN function,
input terminates when the buffer is full or when a terminating character (either
the default character or the character set with the TERMINATOR processing
option) is read.
The following list enumerates the effects on input termination
when you turn on combinations of processing options:
-
BUFFERFULL and TERMINATOR=
- causes input to be terminated when either
of the following is true:
- the buffer is full
- the terminator string is
encountered.
- NOBUFFERFULL and TERMINATOR=
- causes input to be terminated only when
the terminator string is encountered.
- BUFFERFULL (only)
- causes input to be terminated when either
of the following is true:
- the buffer is full
- you press
RETURN.
- NOBUFFERFULL (only)
- causes input to be terminated only when
you press RETURN.
-
TERMINATOR= (only)
- causes input to be terminated only when
the terminator string is encountered.
The
default is NOBUFFERFULL.
-
ECHO | NOECHO
- indicates whether data typed at the terminal
are echoed on the display. If this attribute is not set, the behavior is based
on the LOCALECHO characteristic for the terminal specified with DEVICE=.
The following DCL command shows the characteristics for the terminal:
$ SHOW TERMINAL name
-
SIZE=n
- sets the size of the input buffer (that
is, the number of characters that can be read at one time). The value can
be no more than 32767, the maximum size of a character variable in the SAS
System. The default is 200 characters.
- TERMINATOR=hex-string
- specifies the list of characters that are
considered to be terminating characters for input. Hex-string consists of hexadecimal digit pairs that correspond to the
ASCII value of the characters used as terminators. Do not separate the digit
pairs with delimiters such as commas or spaces.
The terminator character is used only if NOBUFFERFULL
is set. If NOBUFFERFULL is in effect, the default terminator is a carriage
return (hexadecimal value is 0D). If BUFFERFULL is specified, there is no
terminator character and the input is terminated only when the buffer is full.
-
TIMEOUT=n
- specifies how many seconds to wait for input
from the terminal. If no input is received in the time specified, the operation
fails with a time-out error. By default, there is no time limit and the input
operation waits forever.
- channel
- is a numeric variable into which the TTOPEN
function places the channel number.
The channel that
the TTOPEN function assigns is used by the other terminal-access functions
to perform I/O to and from the terminal.
If the TTOPEN function executes successfully, the return value is 0. Otherwise,
the return value is the OpenVMS error
code that indicates why it failed.
The following example reads up to 20 characters, discarding
extra characters when the buffer is full and accepting either the carriage
return or the horizontal tab character (hexadecimal value is 09) as terminators.
If the read is successful, the program prints the string:
length string $ 20;
rc=ttopen("dev=TT: size=20 term=0D09",chan);
rc=ttread(chan,string,size);
if size>0 & rc=0 then put string;
rc=ttclose(chan);
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
