Question

我从xml文件中读取UTF8内容，然后需要按需保存和重新加载。我正在从DavidFaffernan的AssignFile / Writeln / Readln转换为缓冲流：Buffered files (for faster disk access)

我有简单的新WriteLn和ReadLn程序，WriteLn工作，但我无法使ReadLn工作。

我对ReadLn的概念是处理：

读取缓冲区
查找换行符
从PrevPos获取文本到CurrPos-1
保存剩余的缓冲区以添加到下一个读缓冲区的第一行

新的WriteLn程序：

{ * New WriteLn * }
procedure TForm1.Button2Click(Sender: TObject);
var FileOut: TWriteCachedFileStream;
  vText: string;
  vUTF8Text: RawByteString;
begin
  FileOut := TWriteCachedFileStream.Create('c:\tmp\file.txt');
  try
    vText := 'Delphi';
    vUTF8Text := Utf8Encode(vText + sLineBreak);
    FileOut.WriteBuffer(PAnsichar(vUTF8Text)^, Length(vUTF8Text));
    vText := 'VB源码';
    vUTF8Text := Utf8Encode(vText + sLineBreak);
    FileOut.WriteBuffer(PAnsichar(vUTF8Text)^, Length(vUTF8Text));
    vText := 'Java源码';
    vUTF8Text := Utf8Encode(vText + sLineBreak);
    FileOut.WriteBuffer(PAnsichar(vUTF8Text)^, Length(vUTF8Text));
  finally
    FileOut.Free;
  end;
end;

但是Read有问题，因为它无法从文件中读取缓冲区。 TReadOnlyCachedFileStream的读取功能出错：

错误说：

"Project Project1.exe raised exception class $C0000005 with message 'access violation at 0x004069ca: write of address 0x00000010'."


function TReadOnlyCachedFileStream.Read(var Buffer; Count: Longint): Longint;
begin
  ...
  Move(CachePtr^, BufferPtr^, NumOfBytesToCopy); { <- Error occurs here }
  ...
end;

这是我的ReadLn程序 - 无法正常工作，因为我无法解决错误：

{ * New ReadLn * }
procedure TForm1.Button3Click(Sender: TObject);
var FileIn: TReadOnlyCachedFileStream;
  vLinesCounter, vCurrPos, vPrevPos: integer;
  vBuffer: TBytes;
  vUTF8Text, vPrevUTF8Text: string;
  vFilesize,vBytesRead,vNumberOfBytes: Int64;
  vCh: Char;
begin
  vLinesCounter := 0;
  FileIn := TReadOnlyCachedFileStream.Create('c:\tmp\file.txt');
  try
    vFilesize := FileIn.Size;
    while FileIn.Position < vFilesize do
    begin
      vBytesRead:=FileIn.Read(vBuffer, 65536);
      vNumberOfBytes := vNumberOfBytes + vBytesRead;
      {1. Find Line break
       2. Get Text from PrevPos to CurrPos-1
       3. Save rest of buffer to add to first line of next Read buffer}
      vCurrPos := 0; vPrevPos := 0;
      while vCurrPos < vBytesRead do
      begin
        vCh:=Chr(vBuffer[vCurrPos]);
        if (vCh = #13) Or (vCh = #10) then { is New line }
        begin
          if vPrevUTF8Text <> '' then
            vUTF8Text := vPrevUTF8Text + TEncoding.UTF8.GetString(vBuffer, vPrevPos, vCurrPos - 1) { Add previous text that was not separet line}
          else
            vUTF8Text := TEncoding.UTF8.GetString(vBuffer, vPrevPos, vCurrPos - 1);
          vPrevPos := vCurrPos; { Save Pos for next line }
          Inc(vLinesCounter);
          Memo1.Lines.Add(vUTF8Text);
        end;
      end;
      { save rest of text as start of next line }
      if vCurrPos < Length(vBuffer) then
        vPrevUTF8Text := TEncoding.UTF8.GetString(vBuffer, vPrevPos, vCurrPos - 1);
    end;
  finally
    FileIn.Free
  end;
  Memo1.Lines.Add('Lines read: '+IntToStr(vLinesCounter));
end;

Answer 1

RTL在System.Classes单元中有自己的TStreamReader和TStreamWriter类，您应该让他们为您努力工作，例如：

procedure TForm1.Button2Click(Sender: TObject);
var
  FileOut: TStreamWriter;
begin
  FileOut := TStreamWriter.Create('c:\tmp\file.txt', False, TEncoding.UTF8);
  try
    FileOut.WriteLine('Delphi');
    FileOut.WriteLine('VB源码');
    FileOut.WriteLine('Java源码');
  finally
    FileOut.Free;
  end;
end;

procedure TForm1.Button3Click(Sender: TObject);
var
  FileIn: TStreamReader;
  vLinesCounter: Integer;
begin
  vLinesCounter := 0;
  FileIn := TStreamReader.Create('c:\tmp\file.txt', True);
  try
    while not FileIn.EndOfStream do
    begin
      Memo1.Lines.Add(FileIn.ReadLine);
      Inc(vLinesCounter);
    end;
  finally
    FileIn.Free;
  end;
  Memo1.Lines.Add('Lines read: '+IntToStr(vLinesCounter));
end;

如果你想使用David的缓冲类（注意Delphi 10.1 Berlin增加了一个新的TBufferedFileStream类），你仍然可以这样做，例如：

procedure TForm1.Button2Click(Sender: TObject);
var
  FileStrm: TWriteCachedFileStream;
  FileOut: TStreamWriter;
begin
  FileStrm := TWriteCachedFileStream.Create('c:\tmp\file.txt');
  try
    FileOut := TStreamWriter.Create(FileStrm, TEncoding.UTF8);
    try
      FileOut.WriteLine('Delphi');
      FileOut.WriteLine('VB源码');
      FileOut.WriteLine('Java源码');
    finally
      FileOut.Free;
    end;
  finally
    FileStrm.Free;
  end;
end;

procedure TForm1.Button3Click(Sender: TObject);
var
  FileStrm: TReadOnlyCachedFileStream;
  FileIn: TStreamReader;
  vLinesCounter: Integer;
begin
  vLinesCounter := 0;
  FileStrm := TReadOnlyCachedFileStream.Create('c:\tmp\file.txt');
  try
    FileIn := TStreamReader.Create(FileStrm, True);
    try
      while not FileIn.EndOfStream do
      begin
        Memo1.Lines.Add(FileIn.ReadLine);
        Inc(vLinesCounter);
      end;
    finally
      FileIn.Free;
    end;
  finally
    FileStrm.Free;
  end;
  Memo1.Lines.Add('Lines read: '+IntToStr(vLinesCounter));
end;

如何用ReadLn的缓冲流版本替换Readln？

1 个答案: