Re: Newbie Question: using Text_IO.Open() to read from standard input

["Jeffrey R. Carter" <spam@spam.com>]

tmoran@acm.org wrote:

>   Standard Input is already Open when your program starts, so you
> don't need to open it.
>    ARM A.10(4):  "For all Get and Put procedures that operate on text
> files, and for many other subprograms, there are forms with and without a
> file parameter.  ...  If no file is specified, a default input file or a
> default output file is used."  That's simplest, but you might want instead
> to use things from ARM 10.3 "Default Input, Output, and Error Files".

To clarify a little further, you shouldn't open or close standard input. The Get 
and Get_Line procedures that don't take a file parameter read from 
Current_Input. Current_Input is Standard_Input by default. (There's also a 
Current_Output for Put and Put_Line that default to Standard_Output.)

These procedures read from Current_Input rather than Standard_Input to allow a 
program to read from a file if one if provided and from Standard_Input if not:

if Argument_Count > 0 then
    Ada.Text_IO.Open (File => File, Name => Argument (1), ...);
    Ada.Text_IO.Set_Input (File => File);
end if;

loop
    Get_Line (Item => Line, Last => Last);
    -- Use Line
end loop;

if Argument_Count > 0 then
    Ada.Text_IO.Close (File => File);
end if;

-- 
Jeff Carter
"Many times we're given rhymes that are quite unsingable."
Monty Python and the Holy Grail
57