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我遇到了一些使用 TFileStream 将数据块从文件读取到动态数组的 Delphi 代码的问题。编写代码的最初目的是比较两个大小相同但日期和时间戳可能不同的文件的内容，以查看内容是否相同。这是通过将数据对中的每个文件读取到单独的动态数组中并将一个数组的每个字节与另一个数组的相应字节进行比较来完成的。

该代码多次调用 TFileStream.Read。大约 75 次调用后，程序崩溃并显示“内存不足”错误消息。

读取的数据块有多大似乎并不重要，似乎是导致错误消息的调用次数。

该代码是我编写的一个函数，每当程序遇到两个需要比较的文件时都会在其他地方调用该函数（由于我不会深入讨论的原因，这可能是四十或五十个不同的文件对）。'Out of Memory' 错误无论是以小块读取的单个文件，还是以整体方式读取的多个文件，都会发生。似乎调用次数是错误的决定因素。

虽然我意识到实现文件比较的方法可能比我在下面显示的更优雅，但我真正想知道的是使用 TFileStream 和/或 SetLength 调用有什么问题导致记忆问题。我尝试在每次调用后释放内存（如代码所示），似乎没有什么区别。

如果有人能解释出了什么问题，我将不胜感激。

function Compare_file_contents(SPN,TPN : String; SourceFileSize : int64) : boolean;

var

  SF                : TFileStream; //First file of pair for comparison
  TF                : TFileStream; //Second file of pair
  SourceArray       : TBytes; // Buffer array to receive first file data
  TargetArray       : TBytes; //Buffer array to receive second file data
  ArrayLength       : int64; //Length of dynamic array
  Position          : int64; //Position within files to start each block of data read
  TestPosition      : int64; //Position within dynamic arrays to compare each byte
  MaxArrayLength    : integer; //Maximum size for the buffer arrays
  LastRun           : Boolean; //End first repeat loop

begin

{ The comparison has an arbitrary upper boundary of 100 MB to avoid slowing the
  the overall program. The main files bigger than this will be *.pst files that
  will most likely have new dates every time the program is run, so it will take
  about the same time to copy the files as it does to read and compare them, and
  it will have to be done every time.

  The function terminates when it is confirmed that the files are not the same.
  If the source file is bigger than 100 MB, it is simply assumed that they are
  not identical, thus Result = False. Also, LongInt integers (=integers) have
  a range of -2147483648..2147483647, so files bigger than 2 GB will have
  overflowed to a negative number. Hence the check to see if the file size is
  less than zero.

  The outer repeat ... until loop terminates on LastRun, but LastRun should only
  be set if SecondLastRun is True, because it will skip the final comparisons in
  the inner repeat ... until loop otherwise. }

  Result := True;
  LastRun := False;
  MaxArrayLength := 1024*1024;
  if (SourceFileSize > 100*1024*1024) or (SourceFileSize < 0) then Result := False
    else
      begin

{ The comparison is done by using TFileStream to open and read the data from
  the source and target files as bytes to dynamic arrays (TBytes). Then a repeat
  loop is used to compare individual bytes until a difference is found or all
  of the information has been compared. If a difference is found, Result is
  set to False. }

    if SourceFileSize > MaxArrayLength then ArrayLength := MaxArrayLength
      else ArrayLength := SourceFileSize;
    SF := TFileStream.Create(SPN,fmOpenRead);
    TF := TFileStream.Create(TPN,fmOpenRead);
    Position := 0;
    SetLength(SourceArray,ArrayLength);
    SetLength(TargetArray,ArrayLength);
    try
      SF.Read(SourceArray,ArrayLength);
      TF.Read(TargetArray,ArrayLength);
      Position := SF.Position;
    finally
      SF.Free;
      TF.Free;
    end;
      repeat
      TestPosition := 0;
        repeat
          if SourceArray[TestPosition] <> TargetArray[TestPosition] then
            Result := False;
          Inc(TestPosition);
        until (Result = False) or (TestPosition = ArrayLength);
        if SourceFileSize > Position then
          begin
            if SourceFileSize - Position - MaxArrayLength > 0 then
              ArrayLength := MaxArrayLength
              else ArrayLength := SourceFileSize - Position;
            SF := TFileStream.Create(SPN,fmOpenRead);
            TF := TFileStream.Create(TPN,fmOpenRead);
            SF.Position := Position;
            TF.Position := Position;
            try
              SF.Read(SourceArray,ArrayLength);
              TF.Read(TargetArray,ArrayLength);
              Position := SF.Position;
            finally
              SF.Free;
              TF.Free;
            end;
        end else LastRun := True;
      until (Result = False) or LastRun;
      Finalize(SourceArray);
      Finalize(TargetArray);
  end;
end; { Compare_file_contents }
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1 回答 1

6

这个例程似乎比它需要的复杂得多。我没有尝试调试它，而是为您提供了比较流的例程。

function StreamsEqual(Stream1, Stream2: TStream): Boolean;
const
  OneKB = 1024;
var
  Buffer1, Buffer2: array [0..4*OneKB-1] of Byte;
  SavePos1, SavePos2: Int64;
  Count: Int64;
  N: Integer;
begin
  if Stream1.Size<>Stream2.Size then begin
    Result := False;
    exit;
  end;

  SavePos1 := Stream1.Position;
  SavePos2 := Stream2.Position;
  Try
    Stream1.Position := 0;
    Stream2.Position := 0;

    Count := Stream1.Size;
    while Count <> 0 do begin
      N := Min(SizeOf(Buffer1), Count);
      Stream1.ReadBuffer(Buffer1, N);
      Stream2.ReadBuffer(Buffer2, N);
      if not CompareMem(@Buffer1, @Buffer2, N) then begin
        Result := False;
        exit;
      end;
      dec(Count, N);
    end;
    Result := True;
  Finally
    Stream1.Position := SavePos1;
    Stream2.Position := SavePos2;
  End;
end;

如果您希望将 100MB 大小的检查添加到此函数中，很明显在哪里以及如何进行。

上面的例程使用堆栈分配的缓冲区。相反，您的版本在堆上分配。也许您的版本会导致堆碎片。

我意识到这并不能回答您提出的直接问题。但是，它确实解决了您的问题。我希望这被证明是有用的。

于 2013-02-10T15:49:59.380 回答