如何使用API：READFILE

Question

{the data structure for our information}
  Information = record
    Name: array[0..255] of char;
    Title: array[0..255] of char;
    Age: Integer;
  end;var
  Form1: TForm1;implementationprocedure TForm1.Button1Click(Sender: TObject);
var
  FileHandle: THandle;            // a handle to the opened file
  TheInfo: Information;           // holds our information  NumBytesWritten: DWORD;         // variable to track bytes written
  Security: TSecurityAttributes;  // opened file security attributes
begin
  {copy the supplied information to the data structure}
  StrPCopy(TheInfo.Name, Edit1.Text);
  StrPCopy(TheInfo.Title, Edit2.Text);
  TheInfo.Age := StrToInt(Edit3.Text);  {create a generic, binary file}
  Security.nLength := SizeOf(TSecurityAttributes);
  Security.bInheritHandle := FALSE;  FileHandle := CreateFile('TempFile.nfo', GENERIC_WRITE, 0, @Security,
                           CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL or
                           FILE_FLAG_SEQUENTIAL_SCAN, 0);  {write the data in the data structure directly to the file}
  WriteFile(FileHandle, TheInfo, SizeOf(Information), NumBytesWritten, nil);  {implicitly set the end of the file.  this could be used to set
   the end of the file to somewhere in the middle}  SetEndOfFile(FileHandle);  {force any cached file buffers to write the file to disk}
  FlushFileBuffers(FileHandle);  {close the file}
  CloseHandle(FileHandle);
end;procedure TForm1.Button2Click(Sender: TObject);
var
  FileHandle: THandle;             // a handle to the opened file
  TheInfo: Information;            // holds our information
  NumBytesRead: DWORD;             // holds the number of bytes read  Security: TSecurityAttributes;   // opened file security attributes
  TheTitle: array[0..255] of char; // holds a title string
begin
  {open the existing file for reading}
  Security.nLength := SizeOf(TSecurityAttributes);
  Security.bInheritHandle := FALSE;
  FileHandle := CreateFile('TempFile.nfo', GENERIC_READ, 0, @Security,
                           OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL or
                           FILE_FLAG_SEQUENTIAL_SCAN, 0);  {indicate an error if the file does not exist}
  if FileHandle=INVALID_HANDLE_VALUE then
  begin
    ShowMessage('No file exists yet.  Press the ''Write to file'' button to '+
                'create a file.');
    Exit;
  end;  {lock the entire file so no other process may use it}
  LockFile(FileHandle, 0, 0, SizeOf(Information), 0);  {read in a block of information and store it in our data structure}  ReadFile(FileHandle, TheInfo, SizeOf(Information), NumBytesRead, nil);  {display the information}
  Label7.Caption := TheInfo.Name;
  Label8.Caption := TheInfo.Title;
  Label9.Caption := IntToStr(TheInfo.Age);  {the title is located 256 bytes into the file from the beginning (this is
   how long the Name string is), so reposition the file pointer for reading}
  SetFilePointer(FileHandle, SizeOf(TheInfo.Name), nil, FILE_BEGIN);  {read one particular string from the file}  ReadFile(FileHandle, TheTitle, SizeOf(TheTitle), NumBytesRead, nil);  {display the string}
  Label11.Caption := TheTitle;  {unlock and close the file}
  UnlockFile(FileHandle, 0, 0, SizeOf(Information), 0);
  CloseHandle(FileHandle);
end;

Answer 1

procedure ReadString(var Buffer: String);
var
 Readed:Cardinal ;
 Temp:array [0..256] of Char;
 BufferToRead:Cardinal;
begin
 Buffer:='';
 BufferToRead:=1;
 FillChar(Temp,256,0);
  ReadFile(FHandle,Temp,1,Readed,nil) ;
  FIsAtEndOfFile:=Readed=0;
while Temp[0]<>#13 do
 Begin
 FIsAtEndOfFile:=Readed=0;
 if Readed=0 then Exit;
 if Temp[0]<>#10 then Buffer:=Buffer+Temp[0];
 ReadFile(FHandle,Temp,BufferToRead,Readed,nil);
 end;
end;
// 对应我的整个类
Unit MyFileStream;
interface
uses Windows,SysUtils,Dialogs;
type
 TMyFileStream=class
  private
    FFileName: String;
    FHandle: THandle;
    FSize: DWord;
    FIsAtEndOfFile: bool;
    procedure SetFileName(const Value: String);
  published
 property FileName:String read FFileName write SetFileName;
 property Handle:THandle read FHandle;
 property Size:DWord read FSize ;
 property IsAtEndOfFile:bool read FIsAtEndOfFile ;
 public
constructor  Create(_FileName:String;OverWrite:bool=true);
destructor   Destroy;override;
procedure   Write(Buffer:Pointer;Count:Integer);
procedure   WriteLine(Buffer:Pointer;Count:Integer);
procedure   WriteString(var Buffer:String);
procedure    ReadString(var Buffer:String);
procedure    GoToBegin;
procedure    GoToEnd;
procedure    Move(DistanceToMove:Integer);
procedure    Close;
function     Open(_FileName:String;OverWrite:bool=true):bool;
end;
implementationprocedure TMyFileStream.Close;
begin
CloseHandle(FHandle); 
end;constructor TMyFileStream.Create(_FileName: String;OverWrite:bool=true);
begin
FFileName:=_Filename;
if OverWrite then
  Begin
   DeleteFile(_FileName);
   FHandle:=CreateFile(PChar(_FileName),GENERIC_READ or GENERIC_WRITE,
           FILE_SHARE_READ,nil,CREATE_ALWAYS ,FILE_ATTRIBUTE_NORMAL,0)
  end           
   else
  FHandle:=CreateFile(PChar(_FileName),GENERIC_READ or GENERIC_WRITE,
           FILE_SHARE_READ,nil,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0);
if FHandle=INVALID_HANDLE_VALUE then  Raise(Exception.Create(Format('File create/open error!Error Code is %d.',[GetLastError])));
  FSize:=GetFileSize(FHandle,nil);
  FIsAtEndOfFile:=false;
end;destructor TMyFileStream.Destroy;
begin
 CloseHandle(FHandle);
 inherited;
end;procedure TMyFileStream.GoToBegin;
begin
 SetFilePointer(FHandle,0,nil,FILE_BEGIN); 
end;procedure TMyFileStream.GoToEnd;
begin
 SetFilePointer(FHandle,0,nil,FILE_END);
end;procedure TMyFileStream.Move(DistanceToMove: Integer);
begin
 SetFilePointer(FHandle,DistanceToMove,nil,FILE_CURRENT);
end;function TMyFileStream.Open(_FileName: String;OverWrite:bool=true): bool;
begin
Close;
FFileName:=_FileName;
Result:=true;
if OverWrite then
  begin
   DeleteFile(_Filename);
   FHandle:=CreateFile(PChar(_FileName),GENERIC_READ or GENERIC_WRITE,
           FILE_SHARE_READ,nil,CREATE_ALWAYS ,FILE_ATTRIBUTE_NORMAL,0)
  end
             else
  FHandle:=CreateFile(PChar(_FileName),GENERIC_READ or GENERIC_WRITE,
           FILE_SHARE_READ,nil,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0);
if FHandle=INVALID_HANDLE_VALUE then  Raise(Exception.Create(Format('File create/open error!Error Code is %d.',[GetLastError])));
FSize:=GetFileSize(FHandle,nil);
if FHandle=0 then Result:=false;
FIsAtEndOfFile:=false;
end;procedure TMyFileStream.ReadString(var Buffer: String);
var
 Readed:Cardinal ;
 Temp:array [0..256] of Char;
 BufferToRead:Cardinal;
begin
 Buffer:='';
 BufferToRead:=1;
 FillChar(Temp,256,0);
  ReadFile(FHandle,Temp,1,Readed,nil) ;
  FIsAtEndOfFile:=Readed=0;
while Temp[0]<>#13 do
 Begin
 FIsAtEndOfFile:=Readed=0;
 if Readed=0 then Exit;
 if Temp[0]<>#10 then Buffer:=Buffer+Temp[0];
 ReadFile(FHandle,Temp,BufferToRead,Readed,nil);
 end;
end;procedure TMyFileStream.SetFileName(const Value: String);
begin
  FFileName := Value;
  Open(FFileName,true);
end;procedure TMyFileStream.Write(Buffer: Pointer; Count: Integer);
var
 Temp:array[0..255] of Char;
 I:Integer;
begin
 for I:=0 to StrLen(PChar(Buffer))-1 do
  Temp[I]:=Pchar(Buffer)[i];
 FileWrite(FHandle ,Temp,Count);
 FSize:=GetFileSize(FHandle,nil);
end;procedure TMyFileStream.WriteLine(Buffer: Pointer; Count: Integer);
var
 Temp:Array[0..255] of Char;
 I:Integer;
begin
for I:=0 To Count-1 do
 Temp[I]:=PChar(Buffer)[i];
 Temp[Count]:=#13;
 Temp[Count+1]:=#10;
 self.Write(@Temp[0],Count+2);
end;procedure TMyFileStream.WriteString(var Buffer: String);
begin
self.WriteLine(PChar(Buffer),StrLen(PChar(Buffer)));
end;end.