Delphi 正则表达式语法(9): 临界匹配 - 也叫"预搜索"与"反向预搜索"

//匹配右边
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;


//不匹配右边
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;


//匹配左边
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;


//不匹配左边
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;