我在项目中经常使用IN关键字,但是我遇到了很多这样的警告:
[DCC Warning] Unit1.pas(40): W1050 WideChar reduced to byte char in set expressions. Consider using CharInSet function in SysUtils unit.
我进行了一个快速测试,发现使用CharInSet而不是IN会慢65%-100%。
if s1[i] in ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'] then
vs
if CharInSet(s1[i], ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z']) then
以下是两个测试的代码,一个通过循环较短的字符串进行操作,另一个则一次循环较长的字符串:
在表单上添加2个按钮,我已经对短字符串进行了测试:
procedure TForm1.Button1Click(Sender: TObject);
var s1: string;
t1, t2: TStopWatch;
a, i, cnt, vMaxLoop: Integer;
begin
s1 := '[DCC Warning] Unit1.pas(40): W1050 WideChar reduced to byte char in set expressions. Consider using CharInSet function in SysUtils unit.';
vMaxLoop := 10000000;
cnt := 0;
t1 := TStopWatch.Create;
t1.Start;
for a := 1 to vMaxLoop do
for i := 1 to Length(s1) do
if s1[i] in ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'] then
inc(cnt);
t1.Stop;
cnt := 0;
t2 := TStopWatch.Create;
t2.Start;
for a := 1 to vMaxLoop do
for i := 1 to Length(s1) do
if CharInSet(s1[i], ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z']) then
inc(cnt);
t2.Stop;
Button1.Caption := inttostr(t1.ElapsedMilliseconds) + ' - ' + inttostr(t2.ElapsedMilliseconds);
end;
And this for 1 long string:
procedure TForm1.Button2Click(Sender: TObject);
var s1: string;
t1, t2: TStopWatch;
a, i, cnt, vMaxLoop: Integer;
begin
s1 := '[DCC Warning] Unit1.pas(40): W1050 WideChar reduced to byte char in set expressions. Consider using CharInSet function in SysUtils unit.';
s1 := DupeString(s1, 1000000);
s1 := s1 + s1 + s1 + s1; // DupeString is limited, use this to create longer string
cnt := 0;
t1 := TStopWatch.Create;
t1.Start;
for i := 1 to Length(s1) do
if s1[i] in ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'] then
inc(cnt);
t1.Stop;
cnt := 0;
t2 := TStopWatch.Create;
t2.Start;
for i := 1 to Length(s1) do
if CharInSet(s1[i], ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z']) then
inc(cnt);
t2.Stop;
Button2.Caption := inttostr(t1.ElapsedMilliseconds) + ' - ' + inttostr(t2.ElapsedMilliseconds);
end;
为什么他们建议使用更慢的选项,或者我如何在不影响性能的情况下解决这个警告?
s1[i]
是宽字符,则Delphi Win32编译器会为该比较生成正确的代码。我尝试了s1:='Ł'; if(s1[1] in ['A']) then ...
,因为Byte('Ł')=65=Byte('A')
。但是对于这个比较,编译器生成了正确的代码。 - ventiseisord('Ł') = 321
。我查看了CPU窗口,发现完整的字符代码被加载到了EAX
中,没有缩短。 - ventiseis