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如果 Pos 函数的第一个参数是 Char 而非 String, 那么编译器也会先把 Char 转换为 String;

从内存结构到管理机制, String 远比 Char 要复杂.

因此, 面对这种情况(要定位的是 Char) Pos 还有优化的余地; 优化后速度会提升 5 倍左右.

测试效果图:


unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

//自定义的 Pos 函数
function MyPos(c: Char; const str: string): Integer;
var
  i: Integer;
begin
  Result := 0;
  for i := 1 to Length(str) do
    if c = str[i] then begin Result := i; Exit end;
end;

{对比测试}
procedure TForm1.Button1Click(Sender: TObject);
var
  s: string;
  c: Char;
  i: Integer;
  n: Cardinal;
begin
  s := 'abcdefghijklmnopqrstuvwxyz';
  Randomize;
  c := Chr(Random(26) + 97); {随机一个 a..z 的字符}

  {用 Pos 函数}
  n := GetTickCount;
  for i := 1 to 1000000 do Pos(c,s);
  n := GetTickCount - n;
  Text := IntToStr(n) + ' - ';

  {用自定义的 MyPos 函数}
  n := GetTickCount;
  for i := 1 to 1000000 do MyPos(c,s);
  n := GetTickCount - n;
  Text := Text + IntToStr(n);

  Button1.Caption := 'Pos 与 MyPos 速度测试';
end;

end.

posted on 2008-03-18 12:53  万一  阅读(...)  评论(...编辑  收藏