Re: reading a text file into a string

["Nick Roberts" <nick.roberts@acm.org>]

On Thu, 15 Jul 2004 18:49:17 +0100, Marius Amado Alves  
<amado.alves@netcabo.pt> wrote:

> Unbounded_String is the right container for this. But note Get
> for characters skips over newlines and relatives (I think!) Do
> you really want to loose that information? If not then consider
> using Get_Immediate or Get_Line. This assuming you are using
> Ada.Text_IO.

I don't suggest using Get_Immediate for this purpose. You could use:

(a) a combination of Get and the End_of_Line function; or

(b) Get_Line.

Option (a) is likely to be slower, but this might not worry you.

If you use option (b), you must either not care about lines which are too  
long (or know that none are) or you must write special code to deal with  
overlong lines.

Example of option (a):

    c, char: character;
    text : unbounded_string;
    Line_Break: constant Character := Ada.Characters.Latin_1.NUL;
    ...
    -- read in text file
    while not End_of_File(File) loop
       if End_of_Line(File) then
          Append( text, Line_Break );
          Skip_Line(File);
       end if;
       Get( File, c );
       Append( text, c );
    end loop;
    ...
    -- display content of unbounded_string:
    for i in 1..Length(text) loop
       if Element(text,i) = Line_Break then
          Put_Line;
       else
          Put( Element(text,i) );
       end if;
    end loop;

    -- process text
    for i in 1 .. length ( text ) loop
      char := element ( text, i );
      ...
    end loop;

This will work, but it may not be very efficient.

Example of option (b):

    with AI302.Containers.Vectors;
    with Ada.Strings.Unbounded;
    use Ada.Strings.Unbounded;
    ...
    package Line_Vectors is
       new AI302.Containers.Vectors(Positive,Unbounded_String);
    use Line_Vectors;
    ...
    Text: Line_Vectors.Vector_Type;
    Line: String(1..100);
    LL: Natural;
    ...
    -- Read in text file:
    while not End_of_File(File) loop
       Read( File, Line, LL ); -- read line or line segment
       Append( Text, To_Unbounded_String(Line(1..LL)) );
    end loop;
    -- Display content of unbounded_string:
    for i in 1..Natural(Length(Text)) loop
	Put_Line( To_String( Element(Text,i) ) );
    end loop;
    ...

If a line is in the file which is longer than 100 characters, it will be  
broken into two or more lines in the Text variable. Try this yourself.

You can download the AI-302 sample implementation packages from:

    http://home.earthlink.net/~matthewjheaney/charles/ai302-20040227.zip

courtesy of Matthew Heaney (thanks Matt).

-- 
Nick Roberts