HELP | function Is_Open (File : File_Type) return Boolean; package ada.text_io

HELP | function Is_Open (File : File_Type) return Boolean; package ada.text_io

[comicfanzine]

Can someone please post a simple code in which this function is used , i'm lost , thanks .

Re: HELP | function Is_Open (File : File_Type) return Boolean; package ada.text_io

[Niklas Holsti]

On 15-10-26 12:21 , comicfanzine@gmail.com wrote:
> Can someone please post a simple code in which this function is used , i'm lost , thanks .

The following program can be run with or without command-line arguments. 
If, and only if, there are command-line arguments, the program creates 
and writes some text to a file called my_log_file.txt.


with Ada.Command_Line;
with Ada.Text_IO;

procedure Ex_Is_Open
is

    Log_File : Ada.Text_IO.File_Type;
    --
    -- File for log output.
    -- Created only if the program has command-line arguments.


    procedure Log (Text : in String)
    --
    -- Log the Text, if the Log_File is open.
    --
    is
    begin

       if Ada.Text_IO.Is_Open (Log_File) then

          Ada.Text_IO.Put_Line (Log_File, Text);

       end if;

    end Log;


begin  -- Ex_Is_Open

    Log ("This will not appear in the log.");

    if Ada.Command_Line.Argument_Count > 0 then

       Ada.Text_IO.Put_Line ("Creating log file my_log_file.txt.");

       Ada.Text_IO.Create (
          File => Log_File,
          Name => "my_log_file.txt",
          Mode => Ada.Text_IO.Out_File);

    end if;

    Log ("This will appear iff there are command-line arguments.");

    if Ada.Text_IO.Is_Open (Log_File) then
       -- We close the log.
       -- Trying to Close the Log_File if it is not open
       -- raises the exception Ada.Text_IO.Status_Error.

       Ada.Text_IO.Close (Log_File);

    end if;

    Log ("This will not appear in the log.");

end Ex_Is_Open;



-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .

Re: HELP | function Is_Open (File : File_Type) return Boolean; package ada.text_io

[comicfanzine]

Le lundi 26 octobre 2015 11:22:01 UTC+1, comicf...@gmail.com a écrit :
> Can someone please post a simple code in which this function is used , i'm lost , thanks .

Thanks Niklas Holsti ,

I understand but partially , can you explain me in details those lines please? i don't know what you mean by '''Log''' = is that kind of a comment line ? :

line 31 (procedure Ex_Is_Open) =    Log ("This will not appear in the log.");

line 44 (procedure Ex_Is_Open) =    Log ("This will appear iff there are command-line arguments.");

line 55  (procedure Ex_Is_Open) =  Log ("This will not appear in the log.");

Re: HELP | function Is_Open (File : File_Type) return Boolean; package ada.text_io

[Simon Wright]

comicfanzine@gmail.com writes:

> Le lundi 26 octobre 2015 11:22:01 UTC+1, comicf...@gmail.com a écrit :
>> Can someone please post a simple code in which this function is used
> , i'm lost , thanks .
>
> Thanks Niklas Holsti ,
>
> I understand but partially , can you explain me in details those lines
> please? i don't know what you mean by '''Log''' = is that kind of a
> comment line ? :
>
> line 31 (procedure Ex_Is_Open) =    Log ("This will not appear in the log.");
>
> line 44 (procedure Ex_Is_Open) = Log ("This will appear iff there are
> command-line arguments.");
>
> line 55  (procedure Ex_Is_Open) =  Log ("This will not appear in the log.");

If you look at line 13 of Niklas's code you will see the declaration of
'procedure Log'.

If you know C, then - a procedure is like a void function.

But in any case, you need to work through a tutorial. There is a list of
tutorials at http://www.adaic.org/learn/materials/#tutorials - but you
may find AdaTutor (http://zhu-qy.blogspot.co.uk/2012/08/adatutor.html)
more useful.