（寬）字符串 - 存儲在TFileStream，Delphi 7.什麼是最快的方式？

Question

我正在使用Delphi7（非unicode VCL），我需要在TFileStream中存儲很多WideStrings。我不能使用TStringStream，因爲（寬）字符串與二進制數據混合在一起，預計格式會加速加載和寫入數據......但我相信目前我加載/寫入字符串的方式可能是我的代碼的瓶頸...

當前我正在寫一個字符串的長度，然後寫入字符char ... 加載時，首先我加載長度，然後通過字符加載char ...

那麼，什麼是最快的方式來保存和加載WideString到TFileStream？

在此先感謝

Answer 1

而不是讀取和寫一次一個字符，同時讀取和寫入他們都：

procedure WriteWideString(const ws: WideString; stream: TStream); 
var 
    nChars: LongInt; 
begin 
    nChars := Length(ws); 
    stream.WriteBuffer(nChars, SizeOf(nChars); 
    if nChars > 0 then 
    stream.WriteBuffer(ws[1], nChars * SizeOf(ws[1])); 
end; 

function ReadWideString(stream: TStream): WideString; 
var 
    nChars: LongInt; 
begin 
    stream.ReadBuffer(nChars, SizeOf(nChars)); 
    SetLength(Result, nChars); 
    if nChars > 0 then 
    stream.ReadBuffer(Result[1], nChars * SizeOf(Result[1])); 
end; 

現在，在技術上，因爲WideString是Windows BSTR，它可以包含一個奇數字節數。 Length函數讀取字節數併除以2，所以有可能（儘管不太可能）上面的代碼將切斷最後一個字節。你可以使用此代碼來代替：

procedure WriteWideString(const ws: WideString; stream: TStream); 
var 
    nBytes: LongInt; 
begin 
    nBytes := SysStringByteLen(Pointer(ws)); 
    stream.WriteBuffer(nBytes, SizeOf(nBytes)); 
    if nBytes > 0 then 
    stream.WriteBuffer(Pointer(ws)^, nBytes); 
end; 

function ReadWideString(stream: TStream): WideString; 
var 
    nBytes: LongInt; 
    buffer: PAnsiChar; 
begin 
    stream.ReadBuffer(nBytes, SizeOf(nBytes)); 
    if nBytes > 0 then begin 
    GetMem(buffer, nBytes); 
    try 
     stream.ReadBuffer(buffer^, nBytes); 
     Result := SysAllocStringByteLen(buffer, nBytes) 
    finally 
     FreeMem(buffer); 
    end; 
    end else 
    Result := ''; 
end; 

通過Mghie's answer啓發，已經取代了我的Read和Write電話與ReadBuffer和WriteBuffer。如果後者無法讀取或寫入所請求的字節數，則會引發異常。

Answer 2

沒有什麼特別之處寬字符串，閱讀和他們儘可能快地寫你需要一氣呵成讀寫儘可能：

procedure TForm1.Button1Click(Sender: TObject); 
var 
    Str: TStream; 
    W, W2: WideString; 
    L: integer; 
begin 
    W := 'foo bar baz'; 

    Str := TFileStream.Create('test.bin', fmCreate); 
    try 
    // write WideString 
    L := Length(W); 
    Str.WriteBuffer(L, SizeOf(integer)); 
    if L > 0 then 
     Str.WriteBuffer(W[1], L * SizeOf(WideChar)); 

    Str.Seek(0, soFromBeginning); 
    // read back WideString 
    Str.ReadBuffer(L, SizeOf(integer)); 
    if L > 0 then begin 
     SetLength(W2, L); 
     Str.ReadBuffer(W2[1], L * SizeOf(WideChar)); 
    end else 
     W2 := ''; 
    Assert(W = W2); 
    finally 
    Str.Free; 
    end; 
end; 

Answer 3

WideStrings包含WideChar的的「字符串」 ，每個使用2個字節。如果您想要將UTF-16（WideStrings內部使用的）字符串存儲在文件中，並且能夠在其他程序（如記事本）中使用此文件，則需要首先編寫byte order mark：#$FEFF。

如果你知道這一點，寫作可以是這樣的：

Stream1.Write(WideString1[1],Length(WideString)*2); //2=SizeOf(WideChar) 

閱讀可以是這樣的：

Stream1.Read(WideChar1,2);//assert returned 2 and WideChar1=#$FEFF 
SetLength(WideString1,(Stream1.Size div 2)-1); 
Stream1.Read(WideString1[1],(Stream1.Size div 2)-1); 

Answer 4

您還可以使用TFastFileStream讀取數據或字符串，我粘貼單位http://pastebin.com/m6ecdc8c2和下面的示例：

program Project36; 

{$APPTYPE CONSOLE} 

uses 
    SysUtils, Classes, 
    FastStream in 'FastStream.pas'; 

const 
    WideNull: WideChar = #0; 

procedure WriteWideStringToStream(Stream: TFileStream; var Data: WideString); 
var 
    len: Word; 
begin 
    len := Length(Data); 
    // Write WideString length 
    Stream.Write(len, SizeOf(len)); 
    if (len > 0) then 
    begin 
    // Write WideString 
    Stream.Write(Data[1], len * SizeOf(WideChar)); 
    end; 
    // Write null termination 
    Stream.Write(WideNull, SizeOf(WideNull)); 
end; 

procedure CreateTestFile; 
var 
    Stream: TFileStream; 
    MyString: WideString; 
begin 
    Stream := TFileStream.Create('test.bin', fmCreate); 
    try 
    MyString := 'Hello World!'; 
    WriteWideStringToStream(Stream, MyString); 

    MyString := 'Speed is Delphi!'; 
    WriteWideStringToStream(Stream, MyString); 
    finally 
    Stream.Free; 
    end; 
end; 

function ReadWideStringFromStream(Stream: TFastFileStream): WideString; 
var 
    len: Word; 
begin 
    // Read length of WideString 
    Stream.Read(len, SizeOf(len)); 
    // Read WideString 
    Result := PWideChar(Cardinal(Stream.Memory) + Stream.Position); 
    // Update position and skip null termination 
    Stream.Position := Stream.Position + (len * SizeOf(WideChar)) + SizeOf(WideNull); 
end; 

procedure ReadTestFile; 
var 
    Stream: TFastFileStream; 

    my_wide_string: WideString; 
begin 
    Stream := TFastFileStream.Create('test.bin'); 
    try 
    Stream.Position := 0; 
    // Read WideString 
    my_wide_string := ReadWideStringFromStream(Stream); 
    WriteLn(my_wide_string); 
    // Read another WideString 
    my_wide_string := ReadWideStringFromStream(Stream); 
    WriteLn(my_wide_string); 
    finally 
    Stream.Free; 
    end; 
end; 

begin 
    CreateTestFile; 
    ReadTestFile; 
    ReadLn; 
end.