如何创建一个指定大小的文件。

Question

我想建立一个文件，指定文件的大小然后再写入数据。就像网络蚂蚁那样，生成的下载文件一开始就占用了需要的磁盘空间。

Answer 1

filewrite不行吗?
procedure TForm1.Button1Click(Sender: TObject);
var
  BackupName: string;
  FileHandle: Integer;
  StringLen: Integer;
  X: Integer;
  Y: Integer;
begin
  if SaveDialog1.Execute then
  begin
    if FileExists(SaveDialog1.FileName) then
    begin
      BackupName := ExtractFileName(SaveDialog1.FileName);
      BackupName := ChangeFileExt(BackupName, '.BAK');
      if not RenameFile(SaveDialog1.FileName, BackupName) then        raise Exception.Create('Unable to create backup file.');
    end;
    FileHandle := FileCreate(SaveDialog1.FileName);
    { Write out the number of rows and columns in the grid. }
    FileWrite(FileHandle, 
      StringGrid1.ColCount, SizeOf(StringGrid1.ColCount));
    FileWrite(FileHandle, 
      StringGrid1.RowCount, SizeOf(StringGrid1.RowCount));
    for X := 0 to StringGrid1.ColCount ?1 do
    begin      for Y := 0 to StringGrid1.RowCount ?1 do
      begin
        { Write out the length of each string, followed by the string itself. }
        StringLen := Length(StringGrid1.Cells[X,Y]);
        FileWrite(FileHandle, StringLen, SizeOf(StringLen));
        FileWrite(FileHandle,
          StringGrid1.Cells[X,Y], Length(StringGrid1.Cells[X,Y]);
      end;
    end;
    FileClose(FileHandle);
  end;end;

Answer 2

BOOL WriteFile(    HANDLE hFile, // handle to file to write to 
    LPCVOID lpBuffer, // pointer to data to write to file 
    DWORD nNumberOfBytesToWrite, // number of bytes to write 
    LPDWORD lpNumberOfBytesWritten, // pointer to number of bytes written 
    LPOVERLAPPED lpOverlapped  // pointer to structure needed for overlapped I/O
   );

Answer 3

//以下将 temp 分成三个文件 temp1,temp2,temp3
//长度分别为                 10    5    剩下的
procedure TForm1.Button2Click(Sender: TObject);
var
  f:TFileStream;
  m:TMemoryStream;
begin
  f:=TFileStream.Create('d:\temp',fmOpenReadWrite );
//  showmessage(inttostr(f.size));
  f.position:=0;  m:=TMemoryStream.create;
  m.CopyFrom(f,10);
  m.SaveToFile('d:\temp1');  m.size:=0;
  m.CopyFrom(f,5);
  m.SaveToFile('d:\temp2');  m.size:=0;
  m.CopyFrom(f,f.size-15);
  m.SaveToFile('d:\temp3');  m.free;
  f.free;end;

Answer 4

unit mgr;interfaceuses
  Windows, Messages, SysUtils, Classes, Forms,
  StdCtrls,shlobj, Controls, Dialogs,shellapi;type
  TForm1 = class(TForm)
    GroupBox1: TGroupBox;
    Button1: TButton;
    OpenDialog1: TOpenDialog;
    SaveDialog1: TSaveDialog;
    Button3: TButton;
    GroupBox2: TGroupBox;
    ListBox1: TListBox;
    procedure Button1Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure SaveDialog1CanClose(Sender: TObject; var CanClose: Boolean);
    procedure ListBox1DblClick(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    fstream1:tfilestream;
    fstream2:tfilestream;
    list:tstrings;
    len:tstrings;
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.DFM}
const
  flen=136192;  //请注意修改这儿的长度type
  FILE_INFO=record
    filename:array[0..MAX_PATH] of char;
    len:integer;
  end;function SelectDirectory(handle:hwnd;const Caption: string; const Root: WideString;out Directory: string): Boolean;
var
  lpbi:_browseinfo;
  buf:array [0..MAX_PATH] of char;
  id:ishellfolder;
  eaten,att:cardinal;
  rt:pitemidlist;
  initdir:pwidechar;
begin
  result:=false;
  lpbi.hwndOwner:=handle;
  lpbi.lpfn:=nil;
  lpbi.lpszTitle:=pchar(caption);
  lpbi.ulFlags:=BIF_RETURNONLYFSDIRS+BIF_EDITBOX;
  SHGetDesktopFolder(id);
  initdir:=pwchar(root);
  id.ParseDisplayName(0,nil,initdir,eaten,rt,att);
  lpbi.pidlRoot:=rt;
  getmem(lpbi.pszDisplayName,MAX_PATH);
  try
   result:=shgetpathfromidlist(shbrowseforfolder(lpbi),buf);
  except
   freemem(lpbi.pszDisplayName);
  end;
  if result then
  begin
   directory:=buf;
   if length(directory)<>3 then directory:=directory+'\';
  end;
end;procedure TForm1.Button1Click(Sender: TObject);
var
  info:FILE_INFO;
  i:integer;
  buf:array[0..4096] of byte;
  s:integer;
begin
  if savedialog1.Execute then
  if opendialog1.Execute then
  begin
    try
      copyfile(pchar(paramstr(0)),pchar(savedialog1.FileName),false);
      fstream1:=tfilestream.Create(pchar(savedialog1.FileName),fmopenreadwrite);
      fstream1.Seek(flen,soFromBeginning);
      for i:=0 to opendialog1.Files.Count-1 do
      begin
        strpcopy(info.filename,extractfilename(opendialog1.files.strings[i]));
        fstream2:=tfilestream.Create(opendialog1.Files.Strings[i],fmopenread);
        info.len:=fstream2.Size;
        fstream1.Write(info,sizeof(info));
        while fstream2.Position<>fstream2.Size do
        begin
        s:=fstream2.Read(buf,sizeof(buf));
        fstream1.Write(buf,s);
        end;
        fstream2.Free;
      end;
    finally
      fstream1.Free;
    end;
  end;
end;procedure TForm1.Button3Click(Sender: TObject);
var
  f:textfile;
  info:FILE_INFO;
  i:integer;
  buf:array[0..4096] of byte;
  s:integer;
  count,b:integer;
  dir:string;
begin
if selectdirectory(handle,'选择输出文件夹','',dir) then
   try
      fstream1:=tfilestream.Create(paramstr(0),fmShareDenyWrite);
      fstream1.Seek(flen,soFromBeginning);
      while fstream1.Position<>fstream1.Size do
      begin
        fstream1.Read(info,sizeof(info));
        count:=0;
        assignfile(f,dir+info.filename);
        rewrite(f);
        closefile(f);
        fstream2:=tfilestream.Create(dir+info.filename,fmopenwrite);
        fstream2.Size:=0;
        i:=info.len div sizeof(buf);
        for b:=1 to i do
        begin
        s:=fstream1.Read(buf,sizeof(buf));
        fstream2.Write(buf,s);
        inc(count,s);
        end;
        s:=fstream1.Read(buf,info.len-count);
        fstream2.Write(buf,s);
        fstream2.Free;
      end;
    finally
      fstream1.Free;
  end;
end;procedure TForm1.FormCreate(Sender: TObject);
var
  info:FILE_INFO;
begin
   list:=tstringlist.Create;
   len:=tstringlist.Create;
   try
      fstream1:=tfilestream.Create(paramstr(0),fmShareDenyWrite);
      fstream1.Seek(flen,soFromBeginning);
      while fstream1.Position<>fstream1.Size do
      begin
        fstream1.Read(info,sizeof(info));
        list.Add(inttostr(fstream1.position));
        len.Add(inttostr(info.len));
        listbox1.Items.Add(info.filename);
        fstream1.Seek(info.len,soFromCurrent);
      end;
    finally
      fstream1.Free;
  end;
  if listbox1.Items.Count>0 then button3.Enabled:=true else button3.Enabled:=false;
end;procedure TForm1.SaveDialog1CanClose(Sender: TObject;
  var CanClose: Boolean);
var
  f:integer;
begin
  f:=filecreate(savedialog1.FileName);
  if f<=0 then
  begin
    MessageBox(handle,'不能选择输出到该文件！',pchar(application.Title),MB_OK+MB_ICONerror);
    canclose:=false;
  end;
  fileclose(f);
end;procedure TForm1.ListBox1DblClick(Sender: TObject);
var
  path:array[0..max_path] of char;
  filename:string;
  f,b,s,count:integer;
  buf:array[0..4096] of char;
begin
  if button3.Enabled=false then exit;
  gettemppath(Max_path,path);
  filename:=path+listbox1.Items.Strings[listbox1.itemindex];
  fstream1:=tfilestream.Create(paramstr(0),fmShareDenyWrite);
  f:=filecreate(filename);
  fileclose(f);
  count:=0;
  fstream2:=tfilestream.Create(filename,fmopenwrite);
  fstream1.Seek(strtoint(list.Strings[listbox1.ItemIndex]),sofrombeginning);
  f:=strtoint(len.Strings[listbox1.itemindex]) div sizeof(buf);
  for b:=1 to f do
  begin
    s:=fstream1.Read(buf,sizeof(buf));
    fstream2.Write(buf,s);
    inc(count,s);
  end;
  s:=fstream1.Read(buf,strtoint(len.Strings[listbox1.itemindex])-count);
  fstream2.Write(buf,s);
  fstream2.Free;
  shellexecute(handle,'open',pchar(filename),'','',sw_show);
  fstream1.Free;
end;procedure TForm1.FormDestroy(Sender: TObject);
var
 i:integer;
 path:array[0..max_path] of char;
 filename:string;
begin
  list.Free;
  len.Free;
  gettemppath(Max_path,path);
  for i:=0 to listbox1.Items.Count-1 do
  begin
    filename:=path+listbox1.Items.Strings[i];
    deletefile(filename);
  end;
end;

Answer 5

没有作过这样的程序，
学习Ing
接分

Answer 6

有人把delphi的帮助帖了出来，要知道，这段代码在delphi中根本编译不了。

Answer 7

procedure TForm1.Button1Click(Sender: TObject);
var
  F:file of byte;
begin
  AssignFile(F,'F:\1.txt');
  Reset(F);
  Caption:=IntToStr(FileSize(F));
  CloseFile(F);end;procedure TForm1.Button2Click(Sender: TObject);
var
  MemStream:TMemoryStream;
  Len:int64;
begin
  MemStream:=TMemoryStream.Create;
  Len:=1024*1024*100;  //100M的文件
  MemStream.SetSize(Len);
  MemStream.SaveToFile('F:\1.txt');
  MemStream.Free;
end;

Answer 8

还有一个问题，如果能解决我另开个200分帖子给分，有大量的文件要存到硬盘上，过一段时间就要删除一部分。使用一段时间后用windows 的磁盘管理工具查看发现全是红色的碎片，所以我想在生成文件的时候就让文件在物理上是连续的，我想这样就不会出现上述的情况了。大家帮帮忙了。谢谢！

Answer 9

好像在哪里见过你的这个问题，给个思路供你参考，既然你的文件都很大，且大小差不多，不如在存储这些文件时把他们都存为固定大小，比如90～100M的都存为100M，然后把硬盘分为一些区，每个区存储特定大小的文件，100M，120M...

Answer 10

网络蚂蚁/FlashGet在下载文件的时候，会创建这个文件的镜像，如果文件很大，例如一个光盘镜像文件ISO，有650M，此时程序就像死机一样，估计程序在不停的写磁盘~~~~~~：），那么如何快速地创建这种超大的文件呢？看下面的代码：
function CreateFileOnDisk(FileName: string; Size: Int64): Boolean;
{
  在硬盘上面快速创建指定大小的文件
}
var
  F: HFILE;
begin
  Result := not FileExists(FileName);
  if Result then
  begin
    F := FileCreate(FileName, 0);
    SetFilePointer(F, Int64Rec(Size).Lo, @Int64Rec(Size).Hi, FILE_BEGIN);
    SetEndOfFile(F);
    Result := GetLastError = 0;
    FileClose(F);
  end;
end;