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Old 11-01-2011, 03:53 PM   #1
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How do I buffer textinput from file in Ada (Ada newbie)


I am trying to learn Ada/Gnat,and am a bit stuck on the I/O. Maybe someone has a quick tip for me.
I am reprogramming something I had done in C++. Most of it is straightforward, except the input side. Get_Line is much to slow, so I am trying to loop reading into a stringbuffer of, say 50 Mb, , to extract and handle the separate lines later on.

I have tried to use 'read on an unbounded string, but this loads strings with 80 chars at a time and crashes at the end. What is the right way to do this ?
with Ada.Text_IO,Ada.Integer_Text_IO, ada.streams.stream_io,Ada.Strings.Unbounded ;
use Ada.Text_IO,Ada.Integer_Text_IO, ada.streams.stream_io,Ada.Strings.Unbounded  ;
with Ada.Direct_IO;

procedure CompareC is

  subtype unstring is Unbounded_string;
  package unString_IO is new Ada.Direct_IO (unstring);
  chunk: unstring;
  unb_File :  unString_IO.File_type;
  count : integer :=1;
  begin unb_file,unstring_IO.in_file, "testfile" );
     while not unstring_IO.End_of_File( unb_file ) loop   
       unString_IO.Read  (unb_File, Item => chunk); 
-- write etc...
      end  loop;
  unString_IO.Close( unb_file );

end CompareC;
I know, I should really buy the book, but I am just trying if Ada is worth it .Sites like and Big Book of Ada Linux are not very helpful inthis particular thing
Old 11-02-2011, 11:38 AM   #2
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Hi -

Ada "Get_Line" *should* be the best way to go.

If it's "too slow", then I'm guessing the problem might be in the Ada I/O itself. In which case the solution might be to write it something *besides* Ada ("pragma interface" to a C/C++ I/O routine, for example).

Old 11-02-2011, 05:15 PM   #3
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To be more precise, the get_line may not be slow, but on a 1 gig file with lines of less than 300 chars it takes too much time to read the whole file.
In c++ this takes a lot of time as well. That is why, in c++, I replace the getline routine by a read on an ifstream, which puts 50 Mb at a time into memory. I am trying to get that done in Ada.

Last edited by muggabug; 11-02-2011 at 05:18 PM.
Old 11-03-2011, 01:28 AM   #4
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Off: Sadly, on a UNIX platform, if you want performance, you have to do it in C, using read(2) and write(2) system-calls.


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