Question

Lets say I have a String: Go to this page: http://mysite.com/?page=1 , and I have a string page. I would like to create a function like so:

MyBoolean := IsLink('Go to this page: http://mysite.com/?page=1','page',sLink); 
// sLink is a Var, so it would return http://mysite.com/?page=1

Basically it is supposed to check if the word “page” is part of a link or not.

However I just can’t figure it out. Any tips?

Answer 1

You could do something like

function GetLinkContaining(const Str, SubStr: string; out URL: string): boolean;
const
  ValidURLSpecialChars = ['.', ':', '/', '?', '=', '&', '%'];
  Prefixes: array[0..4] of string = ('http://', 'https://', 'ftp://', 'mailto:',
    'www.');

  function IsValidURLChar(const Char: char): boolean;
  begin
    result := IsLetterOrDigit(Char) or (Char in ValidURLSpecialChars);
  end;

var
  SubStrPos: integer;
  Start, &End: integer;
  i: Integer;
  URLBegin: integer;
begin
  result := false;

  URLBegin := 0;
  for i := low(Prefixes) to High(Prefixes) do
  begin
    URLBegin := Pos(Prefixes[i], Str);
    if URLBegin > 0 then
      break;
  end;
  if URLBegin = 0 then Exit(false);

  SubStrPos := PosEx(SubStr, Str, URLBegin);
  if SubStrPos = 0 then Exit(false);

  Start := SubStrPos;
  for i := SubStrPos - 1 downto 1 do
    if IsValidURLChar(Str[i]) then
      dec(Start)
    else
      break;
  &End := SubStrPos + length(SubStr);
  for i := SubStrPos + length(SubStr) to length(Str) do
    if IsValidURLChar(Str[i]) then
      inc(&End)
    else
      break;
  URL := Copy(Str, Start, &End - Start);
  result := true;
end;

To test it:

procedure TForm1.FormCreate(Sender: TObject);
var
  s: string;
begin
  if GetLinkContaining('Go to this page: http://mysite.com/?page=1 (right now!)',
    'page', s) then
    ShowMessage(s);
  if GetLinkContaining('This is my favourite site (www.bbc.co.uk).', 'bbc', s) then
    ShowMessage(s);        
end;