(广角)字符串 - 存储在TFileStream的,德尔福7.什么是最快的方法是什么?
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20-09-2019 - |
题
我使用Delphi7的(非unicode VCL),我需要存储大量一个TFileStream的内部WideStrings的。我不能使用TStringStream为(宽)字符串与二进制数据混合,格式预计将加快加载和写入数据。不过我相信,我加载电流方式/写入字符串可能是一个我的代码瓶颈...
目前我正在写一个字符串的长度,然后写它的焦炭... 同时加载,第一我加载长度,则通过字符...
加载炭那么,什么是保存和加载WideString映射TFileStream的最快方法是什么?
在预先感谢
解决方案
,而不是读取并每次写一个字符,读取和一次他们所有写:
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;
现在,在技术上,因为WideString
是Windows BSTR
,它可以包含一个的奇强>的字节数。该Length
函数读取的字节数和由两部分,因此有可能(尽管不太可能),那上面的代码将切断的最后一个字节。你可以使用此代码来代替:
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;
通过 href="https://stackoverflow.com/questions/1354092/widestring-storing-in-tfilestream-delphi-7-what-is-the-fastest-way/1354122#1354122"> Mghie的回答,更换了Read
和Write
我ReadBuffer
和WriteBuffer
电话。如果它们不能读或写请求的字节数,后者将抛出异常。 其他提示
有什么特别之处宽字符串,阅读和他们尽可能快地写你需要一气呵成读写尽可能多的:
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;
WideStrings含有WideChar的的“字串”,它均使用2个字节。如果你想为UTF-16(WideStrings内部使用)字符串存储在一个文件中,并能够使用此文件中的记事本等其他程序,你需要写的字节顺序标记第一:#$FEFF
如果你知道这一点,写作可以是这样的:
Stream1.Write(WideString1[1],Length(WideString)*2); //2=SizeOf(WideChar)
读数可以是这样的:
Stream1.Read(WideChar1,2);//assert returned 2 and WideChar1=#$FEFF
SetLength(WideString1,(Stream1.Size div 2)-1);
Stream1.Read(WideString1[1],(Stream1.Size div 2)-1);
您还可以使用TFastFileStream用于读取数据或字符串,我粘贴的单元在 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.
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