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

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

[pamela.lum]

Hi,

I need to open a file that is passed to my ada executable as standard
input, in the following fashion:

./myprogram < inputfile.txt

My question is: How can i get the Open() function to open a file from
standard input so that I can bypass using a static file name? For
example:

Integer_File : FILE_TYPE;
Open(Integer_File, In_File, "inputfile.txt"); <-- don't open
inputfile.txt, open file from standard input instead

I know that this can be done easily with Ada.Text_IO.Text_Streams,
however I am stubborn and curious to see if there is a simple and easy
way to do it with the Open() function.

THanks

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

[Anh Vo]

Just use predefined Ada.Command_Line package. The function Argument (1)
should give you the name of the input file (inputfile.txt). Then, you
can open it as mentioned above.

AV

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

[pamela.lum]

Tried that (see the code below named test_cl.ada). It fails to detect
arguments after the redirect ("<" ) character in the command :

./myprogram < inputfile.txt

For example, the output of the code below (test_cl.ada) is as follows:
Input:
./test_cl < inputfile.txt

 The command name : ./test_cl
The number of arguments: 0 <-- does not recognize anything after "<" as
an argument

So why don't i drop the redirect character? Because this is an
assignment and our code will be tested using the redirect.

Suggestions?

CODE FOR DISPLAYING COMMAND LINE ARGUMENTS:
Filename: test_cl.ada

with Ada.Command_Line;
with Gnat.Io; use Gnat.Io;

procedure Test_CL is
begin
   --  Writes out the command name (argv[0])
   Put ("      The command name : ");
   Put (Ada.Command_Line.Command_Name);
   New_Line;

   --  Writes out the number of arguments passed to the program (argc)
   Put ("The number of arguments: ");
   Put (Ada.Command_Line.Argument_Count);
   New_Line;

   --  Writes out all the arguments using the Argument function.
   --  (BE CAREFUL because if the number you pass to Argument is not
   --   in the range 1 .. Argument_Count you will get
Constraint_Error!)
   for I in 1 .. Ada.Command_Line.Argument_Count loop
      Put ("             Argument ");
      Put (I);
      Put (": ");
      Put (Ada.Command_Line.Argument (I));
      New_Line;
   end loop;
end Test_CL;

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

[Anh Vo]

I assumed you took out the < sign. That means < sign is unnecessary.
Command line treats it as the first argument, the file name as second.
I would recommend run it like this  "test_cl inputfile.txt". It should
work. I am absolutely sure of it.

AV

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

[Martin Krischik]

pamela.lum@gmail.com wrote:

> Tried that (see the code below named test_cl.ada). It fails to detect
> arguments after the redirect ("<" ) character in the command :

Most commandline shells will strip the filename which follows "<" and ">"
from the commandline. Instead they will use the filename to open a File an
connect it to Standart_Input or Standart_Output of the newly created
process.

In fact: they will try to open the file *before* the program is started.

Martin

-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com

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

[tmoran]

> I need to open a file that is passed to my ada executable as standard
> input, in the following fashion:
>
> ./myprogram < inputfile.txt
>
> My question is: How can i get the Open() function to open a file from
> standard input so that I can bypass using a static file name?
  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".

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

[pamela.lum]

Heehee...

"Standard Input is already Open when your program starts, so you
don't need to open it. "

Just read that right before you posted. 

Thanks all!

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

[Anh Vo]

I would like to know if your program worked as discussed? Can you
confirm that?

AV

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

[Jeffrey R. Carter]

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

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

[tmoran]

>> to use things from ARM 10.3 "Default Input, Output, and Error Files".
>...
>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:
  Also, sometimes you have code that takes a file, eg
    procedure Process_Data(F : in Ada.Text_IO.File_Type) is ...
and you want to call it with a named file or with Standard Input
    Default_Data : Ada.Text_IO.File_Type;
  begin
    if ... then
      Process_Data(Ada.Text_IO.Standard_Input);
    else
      Ada.Text_IO.Open(Default_Data, ...
      Process_Data(Default_Data);
      Ada.Text_IO.Close(Default_Data);
    end if;

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

[Steve]

<pamela.lum@gmail.com> wrote in message 
news:1129164557.586640.154480@g14g2000cwa.googlegroups.com...
> Hi,
>
> I need to open a file that is passed to my ada executable as standard
> input, in the following fashion:
>
> ./myprogram < inputfile.txt
>
> My question is: How can i get the Open() function to open a file from
> standard input so that I can bypass using a static file name? For
> example:
>
> Integer_File : FILE_TYPE;
> Open(Integer_File, In_File, "inputfile.txt"); <-- don't open
> inputfile.txt, open file from standard input instead
>
> I know that this can be done easily with Ada.Text_IO.Text_Streams,
> however I am stubborn and curious to see if there is a simple and easy
> way to do it with the Open() function.
>
> THanks
>
The following simple example works on red hat linux 8.0

with Ada.Text_IO;

procedure TestPassThru is
  package Text_IO renames Ada.Text_IO;
begin
  while not Text_IO.End_Of_File loop
    declare
        text : String( 1 .. 255 );
        last : Natural;
    begin
       Text_IO.Get_Line( text, last );
       Text_IO.Put_Line( text( 1 .. last ) );
    end;
  end loop;
end TestPassThru;

(Sorry for any typo's I had to copy the code from one screen to another).

Steve
(The Duck)