Delphi中正則表達式語法(9) 臨界匹配 - 預搜索與反向預搜索

//匹配右邊
var
  reg: TPerlRegEx;
begin
  reg := TPerlRegEx.Create(nil);
 
  reg.Subject := 'Delphi 6; Delphi 7; Delphi 2007; Delphi Net';
  reg.RegEx   := 'Delphi (?=2007)'; // ?=
  reg.Replacement := '◆';
  reg.ReplaceAll;
 
  ShowMessage(reg.Subject); //返回: Delphi 6; Delphi 7; ◆2007; Delphi Net
 
  FreeAndNil(reg);
end;
 
//不匹配右邊
var
  reg: TPerlRegEx;
begin
  reg := TPerlRegEx.Create(nil);
 
  reg.Subject := 'Delphi 6; Delphi 7; Delphi 2007; Delphi Net';
  reg.RegEx   := 'Delphi (?!2007)'; // ?!
  reg.Replacement := '◆';
  reg.ReplaceAll;
 
  ShowMessage(reg.Subject); //返回: ◆6; ◆7; Delphi 2007; ◆Net
 
  FreeAndNil(reg);
end;
 
//匹配左邊
var
  reg: TPerlRegEx;
begin
  reg := TPerlRegEx.Create(nil);
 
  reg.Subject := '111, 222, ￥333, ￥444';
  reg.RegEx   := '(?<=￥)\d{3}'; // ?<=
  reg.Replacement := '◆';
  reg.ReplaceAll;
 
  ShowMessage(reg.Subject); //返回: 111, 222, ￥◆, ￥◆
 
  FreeAndNil(reg);
end;
 
//不匹配左邊
var
  reg: TPerlRegEx;
begin
  reg := TPerlRegEx.Create(nil);
 
  reg.Subject := '111, 222, ￥333, ￥444';
  reg.RegEx   := '(?<!￥)\d{3}'; // ?<!
  reg.Replacement := '◆';
  reg.ReplaceAll;
 
  ShowMessage(reg.Subject); //返回: ◆, ◆, ￥333, ￥444
  FreeAndNil(reg);
end;