What's the cause of extra new line with Text_IO when program exit

What's the cause of extra new line with Text_IO when program exit

[Zhu, Qun-Ying]

Hi,

I have known this problem for quite some time, but did not really know 
why it behave like this.

These two programs:
======================================================================
-- hello.adb
with Ada.Text_IO; use Ada.Text_IO;

procedure Hello is
begin
     Put("Hello");
     Put(" ");
     Put("World!");
end Hello;

-- hello_stream.adb
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Text_IO.Text_Streams; use Ada.Text_IO.Text_Streams;

procedure hello_stream is
     std_out   : Stream_Access;
begin
     std_out := Stream (Standard_Output);

     String'Write (std_out, "Hello");
     String'Write (std_out, " ");
     String'Write (std_out, "World!");
end hello_stream;
==================================================================

When executing, they have different behavior.

For hello, you have:
# ./hello
Hello World!
#

While for hello_stream, you got:
# ./hello_stream
Hello World!#

If change the last Put to Put_Line for hello, you got the same result.
I would like to know why it is like that.

Re: What's the cause of extra new line with Text_IO when program exit

[Jeffrey Carter]

On 08/15/2013 06:02 PM, Zhu, Qun-Ying wrote:
>
> When executing, they have different behavior.
>
> For hello, you have:
> # ./hello
> Hello World!
> #
>
> While for hello_stream, you got:
> # ./hello_stream
> Hello World!#
>
> If change the last Put to Put_Line for hello, you got the same result.
> I would like to know why it is like that.

Ada.Text_IO writes to a text file of type Ada.Text_IO.File_Type; Hello writes to 
the file Standard_Output. Text files consist of lines of text; lines are 
conceptually terminated by a line terminator. For a version of Unix such as you 
seem to be using, the conceptual terminator is an actual LF character.

While it is not defined by the language what happens to a File_Type when the 
program ends [ARM A.7(6)], it does require that File_Type have finalization [ARM 
A.10.1(86)]. A logical thing for this finalization to do is to make sure that 
the last line is terminated, and it appears that your implementation does this.

A stream is a different creature than a text file, and doesn't know about lines 
or terminators, so it should not be surprising that it adds no terminator.

-- 
Jeff Carter
"It is the German who is so uncourteous to his verbs."
A Scandal in Bohemia
122

Re: What's the cause of extra new line with Text_IO when program exit

[Dennis Lee Bieber]

On Thu, 15 Aug 2013 20:17:46 -0700, Jeffrey Carter
<spam.jrcarter.not@spam.not.acm.org> declaimed the following:

>While it is not defined by the language what happens to a File_Type when the 
>program ends [ARM A.7(6)], it does require that File_Type have finalization [ARM 
>A.10.1(86)]. A logical thing for this finalization to do is to make sure that 
>the last line is terminated, and it appears that your implementation does this.
>
	Heck, isn't there some mention of also having an EOF marker written?
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

Re: What's the cause of extra new line with Text_IO when program exit

[Jeffrey Carter]

On 08/17/2013 10:54 AM, Dennis Lee Bieber wrote:
> On Thu, 15 Aug 2013 20:17:46 -0700, Jeffrey Carter
> <spam.jrcarter.not@spam.not.acm.org> declaimed the following:
>
>> While it is not defined by the language what happens to a File_Type when the
>> program ends [ARM A.7(6)], it does require that File_Type have finalization [ARM
>> A.10.1(86)]. A logical thing for this finalization to do is to make sure that
>> the last line is terminated, and it appears that your implementation does this.
>>
> 	Heck, isn't there some mention of also having an EOF marker written?

When you close a file, yes. It may not make sense to close standard output.

-- 
Jeff Carter
"This scene's supposed to be in a saloon, but
the censor cut it out. It'll play just as well
this way." [in a soda fountain]
Never Give a Sucker an Even Break
113

Re: What's the cause of extra new line with Text_IO when program exit

[Randy Brukardt]

"Dennis Lee Bieber" <wlfraed@ix.netcom.com> wrote in message 
news:c5ev09h1d6ffg0bbgtqebl4fjt5d567bco@4ax.com...
> On Thu, 15 Aug 2013 20:17:46 -0700, Jeffrey Carter
> <spam.jrcarter.not@spam.not.acm.org> declaimed the following:
>
>>While it is not defined by the language what happens to a File_Type when 
>>the
>>program ends [ARM A.7(6)], it does require that File_Type have 
>>finalization [ARM
>>A.10.1(86)]. A logical thing for this finalization to do is to make sure 
>>that
>>the last line is terminated, and it appears that your implementation does 
>>this.
>>
> Heck, isn't there some mention of also having an EOF marker written?

Right, but there is no requirement in Ada that EOF markers have any 
particular representation. In particular, they might be written as <CR><LF> 
sometimes, and simply "virtual" in other cases. (End-of-page markers are 
almost always handled as "virtual" at the end of files, because no one wants 
every file to end with <FF>.) Janus/Ada never writes any EOF or EOP 
characters at the end of files; Get "manufactures" them if they are not 
present at the end of a file. That makes reading from a text file much more 
complex, but it also means that pretty much any text file can be read with 
Text_IO and it will behave sensibly.

                                            Randy.