高效地将文件读入Pascal AnsiString

Question

我使用此代码将文件内容读取到AnsiString变量中。

var
    c:char;
    f:file of char;
    s:ansistring;
begin
    assign(f,'file');
    reset(f);
        s:='';
        while not eof(f) do
            begin
                read(f,c);
                s:=s+c;
            end;
    close(f);
end;

这段代码运行非常慢。我有一个1MB的文件，程序运行了大约27秒。

如何更快地将文件内容读取到AnsiString？

Answer 1

        begin
            read(f,c);
            s:=s+c;
        end;

您正在读取字符/字符并将其追加到字符串中，这就是您的程序运行缓慢的原因。在单个变量中读取整个文件是不符合逻辑。使用buffer存储文件读取的内容，然后对其进行处理，并释放缓冲区以供下一次读取输入。

program ReadFile;

uses
 Sysutils, Classes;

const
  C_FNAME = 'C:\textfile.txt';

var
  tfIn: TextFile;
  s: string;
  Temp : TStringList;
begin
  // Give some feedback
  writeln('Reading the contents of file: ', C_FNAME);
  writeln('=========================================');
  Temp := TStringList.Create;
  // Set the name of the file that will be read
  AssignFile(tfIn, C_FNAME);

  // Embed the file handling in a try/except block to handle errors gracefully
  try
    // Open the file for reading
    reset(tfIn);

    // Keep reading lines until the end of the file is reached
    while not eof(tfIn) do
    begin
      readln(tfIn, s);
      Temp.Append(s);
    end;

    // Done so close the file
    CloseFile(tfIn);

    writeln(temp.Text);
  except
    on E: EInOutError do
     writeln('File handling error occurred. Details: ', E.Message);
  end;


  //done clear the TStringList
   temp.Clear;
   temp.Free;   

  // Wait for the user to end the program
  writeln('=========================================');
  writeln('File ', C_FNAME, ' was probably read. Press enter to stop.');
  readln;
end.   

在File Handling in Pascal上有更多示例