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HOSTS file parsing

Posted on 2011-09-12
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Last Modified: 2012-05-12
From file sample posted below I would like to get TStringList with items:
127.0.0.1 losalhost
127.0.0.1 sampleone.com
127.0.0.1 sampletwo.com
127.0.0.1 samplethree.com

So, a parsing routine needed that ignores all commented (#) lines and recognizes multiple hosts in one line.
# Copyright (c) 1993-2009 Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# space.
#
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
#
# For example:
#
#      102.54.94.97     rhino.acme.com          # source server
#       38.25.63.10     x.acme.com              # x client host
# localhost name resolution is handled within DNS itself.
#	127.0.0.1       localhost
#	::1             localhost
127.0.0.1       localhost
127.0.0.1 sampleone.com sampletwo.com samplethree.com # comment

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Question by:3axap
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3 Comments
 
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Accepted Solution

by:
epasquier earned 500 total points
ID: 36521682
assuming you have the HOSTS file loaded in a Memo, here is how to put the hosts found, both in a listbox (= TstringList) as you asked, and in a TreeView
procedure TForm1.btnGetHostsClick(Sender: TObject);
var
 i,P,P2:integer;
 L:String;
 HostList:TStringList;
 Node:TTreeNode; // we will add found values in a treeview
begin
 HostList:=TStringList.Create;
 HostList.Delimiter:=' '; // delimiter will be a space
 for i := 0 to Memo.Lines.Count-1 do
  begin
   L:=Trim(Memo.Lines[i]);
   P:=Pos('#',L);
   if P>0 then L:=Trim(Copy(L,1,P-1));
   L:=StringReplace(L,#8,' ',[rfReplaceAll]); // Replace tabs
   P:=Length(L);
   Repeat
    L:=StringReplace(L,'  ',' ',[rfReplaceAll]); // Strip dup spaces
    P2:=Length(L);
    if P=P2 then break; // Exit when no replace occured
    P:=P2;
   Until False; // Infinite Loop
   HostList.DelimitedText:=L;
   if HostList.Count>1 then
    begin
     Node:=TreeView.Items.Add(nil,HostList[0]); // Add in a treeview
     for P := 1 to HostList.Count-1 do
      begin
       TreeView.Items.AddChild(Node,HostList[P]); // add child in the treeview
       ListBox.Items.Add(HostList[0]+' '+HostList[P]); // add in a listbox
      end;
    end;
  end;
 HostList.Free;
end;

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Author Closing Comment

by:3axap
ID: 36521870
Thank you Pasquier.
One related question if I may. What is the best practice to open text file for reading, as in my original question?
Read it to TStringList to Memo or to TFileStream?
Thanks
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LVL 25

Expert Comment

by:epasquier
ID: 36522054
Memo.Lines.LoadFromFile( aFileName );

if you don't need to display in a memo, use a TStringList :
aStringList.LoadFromFile( aFileName );
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