Delphi - 如何使用启动/停止功能以毫秒或纳秒为单位制作定时器？

Question

我在Delphi7中寻找一个以毫秒或纳秒为单位的计时器.我必须通过顺序搜索检查三个ISAM文件的速度.第一个ind文件包含50个字符串,如"record_0"到"record_50".第二个 - "record_0"到"record_500",第三个 - "record_0"到"record_5000".我实现了一切,但我不知道如何制作计时器.我正在比较一个字符串与每个ISAM文件中的最后一项.这是我的第一个ind文件的代码:

procedure TForm1.Button1Click(Sender: TObject);
  var i:integer;
  var content : String[20];
  var indexCounter:integer;
  var keyword:string;
begin
  //First ISAM file
  AssignFile(indF1, 'index1.ind');
  ReWrite(indF1);
  Reset(indF1);
  for i:=0 to 49 do begin
    content := 'record_';
    content := content + IntToStr(i+1);
    index1.index1 := content;
    index1.position1 := FileSize(indF1);
    Seek(indF1, FileSize(indF1));
    write(indF1, index1);
  end;
  CloseFile(indF1);
  Label12.Caption := FileSizeStr('index1.ind');

  //Sequential search in first ind file
  Reset(indF1);
  keyword := 'record_50';
  indexCounter := 0;
  //start timer
  while not Eof(indF1) do begin
    Seek(indF1, indexCounter);
    Read(indF1, Index1);
    if (keyword = Index1.index1) then begin
      //stop timer;
      //Label20 := milliseconds/nanoseconds;
      //return/break while loop (result := -1; exit;) ???
    end;
    indexCounter := indexCounter + 1;
  end;

我需要一个过程/函数,以便在调用它时它应该以毫秒或纳秒开始计数,并在找到字符串时停止(它是每个ind文件中的最后一个字符串)并显示遍历所有文件的经过时间.另外我不知道如何打破while循环.提前致谢.

Answer 1

TStopWatch这里描述的类"delphi-high-performance-timer-tstopwatch"具有所需的所有功能(对于Delphi-7).

它在后来的Delphi版本(Delphi-2010)中实现,作为单元诊断的高级记录.

例:

var
  sw : TStopWatch;
  elapsedMilliseconds : cardinal;
begin
  ...
  sw := TStopWatch.Create() ;
  try
    sw.Start;

    while not Eof(indF1) do begin
      Seek(indF1, indexCounter);
      Read(indF1, Index1);
      if (keyword = Index1.index1) then begin
        sw.Stop;
        Label20.Caption := IntToStr(sw.ElapsedMilliseconds);
        break; // break while loop
      end;
      indexCounter := indexCounter + 1;
    end;
    ...
  finally
    sw.Free;
  end;
end;

要打破while循环,只需break;在条件测试中进行.

Answer 2

使用QueryPerformanceFrequency和QueryPerformanceCounter.第一个函数每秒返回一个单位,第二个函数返回一个值.

lFreq: Int64;
InitialF, FinalF: Int64;

if QueryPerformanceFrequency(lFreq) then
  // hi-res timer is supported
else
  // hi-res timer is not supported

QueryPerformanceCounter(InitialF);
// do something you want to time
QueryPerformanceCounter(FinalF);
// duration of the time of something is FinalF - InitialF in "units"
// divide by lFreq to get the amount of time in seconds, 
// this will be an Extended type.