Delphi Memory-Mapped File简单示例

{
Copyright ?1999 by Delphi 5 Developer‘s Guide - Xavier Pacheco and Steve Teixeira
}

unit MainFrm;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls,
  Forms, Dialogs, StdCtrls;

const
  FName = ‘test.txt‘;

type

  TMainForm = class(TForm)
    btnUpperCase: TButton;
    memTextContents: TMemo;
    lblContents: TLabel;
    btnLowerCase: TButton;
    procedure btnUpperCaseClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure btnLowerCaseClick(Sender: TObject);
  public
    UCase: Boolean;
    procedure ChangeFileCase;
  end;

var
  MainForm: TMainForm;

implementation

{$R *.DFM}

procedure TMainForm.btnUpperCaseClick(Sender: TObject);
begin
  UCase := True;
  ChangeFileCase;
end;

procedure TMainForm.btnLowerCaseClick(Sender: TObject);
begin
  UCase := False;
  ChangeFileCase;
end;

procedure TMainForm.FormCreate(Sender: TObject);
begin
  memTextContents.Lines.LoadFromFile(FName);
  // Change to upper case by default.
  UCase := True;
end;

procedure TMainForm.ChangeFileCase;
var
  FFileHandle: THandle; // Handle to the open file.
  FMapHandle: THandle;  // Handle to a file-mapping object
  FFileSize: Integer;   // Variable to hold the file size.
  FData: PByte;         // Pointer to the file‘s data when mapped.
  PData: PChar;         // Pointer used to reference the file data.
begin

  { First obtain a file handle to the file to be mapped. This code
    assumes the existence of the file. Otherwise, you can use the
    FileCreate() function to create a new file. }

  if not FileExists(FName) then
    raise Exception.Create(‘File does not exist.‘)
  else
    FFileHandle := FileOpen(FName, fmOpenReadWrite);

  // If CreateFile() was not successful, raise an exception
  if FFileHandle = INVALID_HANDLE_VALUE then
    raise Exception.Create(‘Failed to open or create file‘);

  try
    { Now obtain the file size which we will pass to the other file-
      mapping functions. We‘ll make this size one byte larger as we
      need to append a null-terminating character to the end of the
      mapped-file‘s data.}
    FFileSize := GetFileSize(FFileHandle, Nil);

   { Obtain a file-mapping object handle. If this function is not
      successful, then raise an exception. }
    FMapHandle := CreateFileMapping(FFileHandle, nil,
       PAGE_READWRITE, 0, FFileSize, nil);

    if FMapHandle = 0 then
      raise Exception.Create(‘Failed to create file mapping‘);
  finally
    // Release the file handle
    CloseHandle(FFileHandle);
  end;

  try
    { Map the file-mapping object to a view. This will return a pointer
      to the file data. If this function is not successful, then raise
      an exception. }
    FData := MapViewOfFile(FMapHandle, FILE_MAP_ALL_ACCESS, 0, 0, FFileSize);

    if FData = Nil then
      raise Exception.Create(‘Failed to map view of file‘);

  finally
    // Release the file-mapping object handle
    CloseHandle(FMapHandle);
  end;

  try
    { !!! Here is where you would place the functions to work with
    the mapped file‘s data. For example, the following line forces
    all characters in the file to uppercase }
    PData := PChar(FData);
    // Position the pointer to the end of the file‘s data
    inc(PData, FFileSize);

    // Append a null-terminating character to the end of the file‘s data
    PData^ := #0;

    // Now set all characters in the file to uppercase
    if UCase then
      StrUpper(PChar(FData))
    else
      StrLower(PChar(FData));

  finally
    // Release the file mapping.
    UnmapViewOfFile(FData);
  end;
  memTextContents.Lines.Clear;
  memTextContents.Lines.LoadFromFile(FName);
end;

end.