delphi-重写文件实际上做了什么？

Question

Rewrite 是否会清除现有文件的文件内容，还是将其删除并创建一个新文件？我的 app.exe 文件夹中有一个文本文件，我需要清除该文件。有什么例子吗？

Answer 1

来自 Delphi XE2 文档，主题 Rewrite - 阅读最后引用的段落:

Creates a new file and opens it.

In Delphi code, Rewrite creates a new external file with the name assigned to F.

F is a variable of any file type associated with an external file using AssignFile. RecSize is an optional expression that can be specified only if F is an untyped file. If F is an untyped file, RecSize specifies the record size to be used in data transfers. If RecSize is omitted, a default record size of 128 bytes is assumed.

If an external file with the same name already exists, it is deleted and a new empty file is created in its place.

在同一文档中，页面底部的 System.Rewrite 链接已修改为使用您应用的文件夹:

procedure TForm1.Button1Click(Sender: TObject);
var 
  F: TextFile;
  AppDir: string;
begin
  // Instead of ParamStr(0), you can use Application.ExeName
  // if you prefer
  AppDir := ExtractFilePath(ParamStr(0)); 
  AssignFile(F, AppDir + 'NEWFILE.$$$');
  Rewrite(F);  // default record size is 128 bytes
  Writeln(F, 'Just created file with this text in it...');
  CloseFile(F);
  MessageDlg('NEWFILE.$$$ has been created in the ' + AppDir + ' directory.',
    mtInformation, [mbOk], 0, mbOK);
end;

不过，您应该知道，Rewrite 已经过时并且不支持 Unicode。您应该使用更现代的方法来读取和写入文件，例如 TFileStream或TStringWriter (甚至是 TStringList 的简单解决方案)。

var
  SL: TStringList;
  AppDir: string;
begin
  AppDir := ExtractFilePath(ParamStr(0));
  SL := TStringList.Create;
  try
    SL.Add('Just created file with this text in it...');
    // Add more lines here if needed, and then only save once
    SL.SaveToFile(AppDir + 'NEWFILE.$$$');
    MessageDlg('NEWFILE.$$$ has been created in the ' + AppDir + ' directory.',
      mtInformation, [mbOk], 0, mbOK);
  finally
    SL.Free;
  end;
end;

请注意，您不能使用TStrings；这是一个抽象类。您需要使用它的后代之一(TStringList 是最常用的)。