# 《Delphi 算法与数据结构》学习与感悟[4]: 关于 const

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}

//判断一个字符串中数字的个数
function GetNum1(str: string): Integer;
var
i: Integer;
begin
Result := 0;
for i := 1 to Length(str) do
if str[i] in ['0'..'9'] then Inc(Result);
end;

//同样的函数只是给参数加上 const
function GetNum2(const str: string): Integer;
var
i: Integer;
begin
Result := 0;
for i := 1 to Length(str) do
if str[i] in ['0'..'9'] then Inc(Result);
end;

{对比测试}
procedure TForm1.Button1Click(Sender: TObject);
var
s: string;
n: Cardinal;
i: Integer;
begin
s := 'ABC123';

n := GetTickCount;
for i := 0 to 1000000 do GetNum1(s);
n := GetTickCount - n;
Text := IntToStr(n) + ' - ';

n := GetTickCount;
for i := 0 to 1000000 do GetNum2(s);
n := GetTickCount - n;
Text := Text + IntToStr(n);
end;

end.


posted on 2008-03-18 10:55  万一  阅读(...)  评论(...编辑  收藏