从文本文件中修改或删除一行是低级的方式吗? [英] Modifying or deleting a line from a text file the low-level way?
问题描述
我正在使用Delphi中的文本文件,我不希望使用加载/保存字符串列表的方法。我打算保留一个开放的filestream,在那里我读和写我的数据,保留大量的数据在硬盘而不是内存。我有一个简单的概念,将新行写入文本文件并阅读它们,但是当涉及修改和删除它们时,我找不到任何好的资源。
I'm working with a Text File in Delp and I don't wish to use the method of loading/saving with a string list. I intend to maintain an open filestream where I read and write my data there, keeping massive amounts of data on the hard disk instead of in the memory. I have the simple concept of writing new lines to a text file and reading them, but when it comes to modifying and deleting them, I cannot find any good resources.
每个该文件中的行包含一个名称和等号,其余的是数据。例如, SOMEUNIQUENAME = SomeStringValue
。我打算在线程内保持文件一段时间。该线程执行传入请求以获取,设置或删除某些数据字段。我在循环中使用 WriteLn
和 ReadLn
,评估 EOF
。以下是我如何读取数据的示例:
Each line in this file contains a name, and equals sign, and the rest is data. For example, SOMEUNIQUENAME=SomeStringValue
. I intend to keep a file open for a period of time inside of a thread. This thread performs incoming requests to either get, set, or delete certain fields of data. I use WriteLn
and ReadLn
in a loop, evaluating EOF
. Below is an example of how I read the data:
FFile = TextFile;
...
function TFileWrapper.ReadData(const Name: String): String;
var
S: String; //Temporary line to be parsed
N: String; //Temporary name of field
begin
Result:= '';
Reset(FFile);
while not EOF(FFile) do begin
ReadLn(FFile, S);
N:= UpperCase(Copy(S, 1, Pos('=', S)-1));
if N = UpperCase(Name) then begin
Delete(S, 1, Pos('=', S));
Result:= S;
Break;
end;
end;
end;
...然后我触发一个事件,通知发件人结果。请求位于队列内,这是这些请求的消息泵。线程简单地重复处理队列中的下一个请求,与典型应用程序的工作方式类似。
...and then I trigger an event which informs sender of result. The requests are inside of a queue, which is sort of a message pump for these requests. The thread simply processes the next request in the queue repeatedly, similar to how typical applications work.
我有程序准备好能够写入和删除这些字段,但是不知道我该怎么做才能真正对文件执行操作。
I have procedures ready to be able to write and delete these fields, but I don't know what I have to do to actually perform the action on the file.
procedure TFileWrapper.WriteData(const Name, Value: String);
var
S: String; //Temporary line to be parsed
N: String; //Temporary name of field
begin
Result:= '';
Reset(FFile);
while not EOF(FFile) do begin
ReadLn(FFile, S);
N:= UpperCase(Copy(S, 1, Pos('=', S)-1));
if N = UpperCase(Name) then begin
//How to re-write this line?
Break;
end;
end;
end;
procedure TFileWrapper.DeleteData(const Name: String);
var
S: String; //Temporary line to be parsed
N: String; //Temporary name of field
begin
Result:= '';
Reset(FFile);
while not EOF(FFile) do begin
ReadLn(FFile, S);
N:= UpperCase(Copy(S, 1, Pos('=', S)-1));
if N = UpperCase(Name) then begin
//How to delete this line?
Break;
end;
end;
end;
最后,我需要避免将整个文件加载到内存中才能完成此操作
In the end, I need to avoid loading the entire file into the memory to be able to accomplish this.
推荐答案
我发现这是一个有趣的问题,所以我做了一个小型的控制台应用程序。
I find this an interesting question, so I made a small console app.
我使用3种方法:
- TStringList
- Streamreader / StreamWriter
-
- 文本文件
所有方法都是定时重复100次,文本文件大小为10kb和大小为1Mb的文本文件。
这是程序:
All methods are timed and repeated 100 times with a text file of 10kb in size and a text file 1Mb in size. Here is the program:
program Project16;
{$APPTYPE CONSOLE}
uses
SysUtils, Classes, StrUtils, Diagnostics, IOUtils;
procedure DeleteLine(StrList: TStringList; SearchPattern: String);
var
Index : Integer;
begin
for Index := 0 to StrList.Count-1 do
begin
if ContainsText(StrList[Index], SearchPattern) then
begin
StrList.Delete(Index);
Break;
end;
end;
end;
procedure DeleteLineWithStringList(Filename : string; SearchPattern : String);
var StrList : TStringList;
begin
StrList := TStringList.Create;
try
StrList.LoadFromFile(Filename);
DeleteLine(StrList, SearchPattern);
// don't overwrite our input file so we can test
StrList.SaveToFile(TPath.ChangeExtension(Filename, '.new'));
finally
StrList.Free;
end;
end;
procedure DeleteLineWithStreamReaderAndWriter(Filename : string; SearchPattern : String);
var
Reader : TStreamReader;
Writer : TStreamWriter;
Line : String;
DoSearch : Boolean;
DoWrite : Boolean;
begin
Reader := TStreamReader.Create(Filename);
Writer := TStreamWriter.Create(TPath.ChangeExtension(Filename, '.new'));
try
DoSearch := True;
DoWrite := True;
while Reader.Peek >= 0 do
begin
Line := Reader.ReadLine;
if DoSearch then
begin
DoSearch := not ContainsText(Line, SearchPattern);
DoWrite := DoSearch;
end;
if DoWrite then
Writer.WriteLine(Line)
else
DoWrite := True;
end;
finally
Reader.Free;
Writer.Free;
end;
end;
procedure DeleteLineWithTextFile(Filename : string; SearchPattern : String);
var
InFile : TextFile;
OutFile : TextFile;
Line : String;
DoSearch : Boolean;
DoWrite : Boolean;
begin
AssignFile(InFile, Filename);
AssignFile(OutFile, TPath.ChangeExtension(Filename, '.new'));
Reset(InFile);
Rewrite(OutFile);
try
DoSearch := True;
DoWrite := True;
while not EOF(InFile) do
begin
Readln(InFile, Line);
if DoSearch then
begin
DoSearch := not ContainsText(Line, SearchPattern);
DoWrite := DoSearch;
end;
if DoWrite then
Writeln(OutFile, Line)
else
DoWrite := True;
end;
finally
CloseFile(InFile);
CloseFile(OutFile);
end;
end;
procedure TimeDeleteLineWithStreamReaderAndWriter(Iterations : Integer);
var
Count : Integer;
Sw : TStopWatch;
begin
Writeln(Format('Delete line with stream reader/writer - file 10kb, %d iterations', [Iterations]));
Sw := TStopwatch.StartNew;
for Count := 1 to Iterations do
DeleteLineWithStreamReaderAndWriter('c:\temp\text10kb.txt', 'thislinewillbedeleted=');
Sw.Stop;
Writeln(Format('Elapsed time : %d milliseconds', [Sw.ElapsedMilliseconds]));
Writeln(Format('Delete line with stream reader/writer - file 1Mb, %d iterations', [Iterations]));
Sw := TStopwatch.StartNew;
for Count := 1 to Iterations do
DeleteLineWithStreamReaderAndWriter('c:\temp\text1Mb.txt', 'thislinewillbedeleted=');
Sw.Stop;
Writeln(Format('Elapsed time : %d milliseconds', [Sw.ElapsedMilliseconds]));
end;
procedure TimeDeleteLineWithStringList(Iterations : Integer);
var
Count : Integer;
Sw : TStopWatch;
begin
Writeln(Format('Delete line with TStringlist - file 10kb, %d iterations', [Iterations]));
Sw := TStopwatch.StartNew;
for Count := 1 to Iterations do
DeleteLineWithStringList('c:\temp\text10kb.txt', 'thislinewillbedeleted=');
Sw.Stop;
Writeln(Format('Elapsed time : %d milliseconds', [Sw.ElapsedMilliseconds]));
Writeln(Format('Delete line with TStringlist - file 1Mb, %d iterations', [Iterations]));
Sw := TStopwatch.StartNew;
for Count := 1 to Iterations do
DeleteLineWithStringList('c:\temp\text1Mb.txt', 'thislinewillbedeleted=');
Sw.Stop;
Writeln(Format('Elapsed time : %d milliseconds', [Sw.ElapsedMilliseconds]));
end;
procedure TimeDeleteLineWithTextFile(Iterations : Integer);
var
Count : Integer;
Sw : TStopWatch;
begin
Writeln(Format('Delete line with text file - file 10kb, %d iterations', [Iterations]));
Sw := TStopwatch.StartNew;
for Count := 1 to Iterations do
DeleteLineWithTextFile('c:\temp\text10kb.txt', 'thislinewillbedeleted=');
Sw.Stop;
Writeln(Format('Elapsed time : %d milliseconds', [Sw.ElapsedMilliseconds]));
Writeln(Format('Delete line with text file - file 1Mb, %d iterations', [Iterations]));
Sw := TStopwatch.StartNew;
for Count := 1 to Iterations do
DeleteLineWithTextFile('c:\temp\text1Mb.txt', 'thislinewillbedeleted=');
Sw.Stop;
Writeln(Format('Elapsed time : %d milliseconds', [Sw.ElapsedMilliseconds]));
end;
begin
try
TimeDeleteLineWithStringList(100);
TimeDeleteLineWithStreamReaderAndWriter(100);
TimeDeleteLineWithTextFile(100);
Writeln('Press ENTER to quit');
Readln;
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
end.
输出:
Delete line with TStringlist - file 10kb, 100 iterations
Elapsed time : 188 milliseconds
Delete line with TStringlist - file 1Mb, 100 iterations
Elapsed time : 5137 milliseconds
Delete line with stream reader/writer - file 10kb, 100 iterations
Elapsed time : 456 milliseconds
Delete line with stream reader/writer - file 1Mb, 100 iterations
Elapsed time : 22382 milliseconds
Delete line with text file - file 10kb, 100 iterations
Elapsed time : 250 milliseconds
Delete line with text file - file 1Mb, 100 iterations
Elapsed time : 9656 milliseconds
Press ENTER to quit
正如您所看到的,TStringList是赢家。
由于您无法使用TStringList,所以TextFile不是一个坏的选择...
As you can see is TStringList the winner here. Since you are not able to use TStringList, TextFile is not a bad choice after all...
P.S。 :此代码省略了您必须删除输入文件的部分,并将输出文件重命名为原始文件名
P.S. : this code omits the part where you have to delete the inputfile and rename the outputfile to the original filename
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