linux结构体指针强制转换,关于结构体与类型转换的一点小技巧

unit Unit1;

interface

uses

Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

Dialogs, StdCtrls;

type

TForm1 = class(TForm)

Button1: TButton;

Button2: TButton;

Button3: TButton;

Button4: TButton;

Button5: TButton;

procedure Button1Click(Sender: TObject);

procedure Button2Click(Sender: TObject);

procedure Button3Click(Sender: TObject);

procedure Button4Click(Sender: TObject);

procedure Button5Click(Sender: TObject);

end;

var

Form1: TForm1;

implementation

{$R *.dfm}

type {下面两个结构体的大小都是 4 字节, 相当于一个 Cardinal 或 Integer 或 DWORD 的大小}

TMyByteStruct = record

b1: Byte;

b2: Byte;

b3: Byte;

b4: Byte;

end;

TMyWordStruct = record

w1: Word;

w2: Word;

end;

procedure TForm1.Button1Click(Sender: TObject);

var

ByteStruct: TMyByteStruct;

num: Cardinal;

begin

{假如}

ByteStruct.b1 := $A1;

ByteStruct.b2 := $B2;

ByteStruct.b3 := $C3;

ByteStruct.b4 := $D4;

{那么}

num := Cardinal(ByteStruct);

ShowMessageFmt('$%x', [num]); //$D4C3B2A1

end;

procedure TForm1.Button2Click(Sender: TObject);

var

WordStruct: TMyWordStruct;

num: Cardinal;

begin

{假如}

WordStruct.w1 := $ABCD;

WordStruct.w2 := $1234;

{那么}

num := Cardinal(WordStruct);

ShowMessageFmt('$%x', [num]); //$1234ABCD

end;

procedure TForm1.Button3Click(Sender: TObject);

var

num: Cardinal;

ByteStruct: TMyByteStruct;

begin

num := $ABCD1234;

Cardinal(ByteStruct) := num;

//ByteStruct := TMyByteStruct(num); {这同上一句}

ShowMessageFmt('$%x', [ByteStruct.b1]); //$34

ShowMessageFmt('$%x', [ByteStruct.b2]); //$12

ShowMessageFmt('$%x', [ByteStruct.b3]); //$CD

ShowMessageFmt('$%x', [ByteStruct.b4]); //$AB

end;

procedure TForm1.Button4Click(Sender: TObject);

var

num: Cardinal;

WordStruct: TMyWordStruct;

begin

num := $ABCD1234;

Cardinal(WordStruct) := num;

//WordStruct := TMyWordStruct(num); {这同上一句}

ShowMessageFmt('$%x', [WordStruct.w1]); //$1234

ShowMessageFmt('$%x', [WordStruct.w2]); //$ABCD

end;

procedure TForm1.Button5Click(Sender: TObject);

var

ByteStruct: TMyByteStruct;

WordStruct: TMyWordStruct;

begin

WordStruct.w1 := $2211;

WordStruct.w2 := $4433;

Cardinal(ByteStruct) := Cardinal(WordStruct);

//ByteStruct := TMyByteStruct(WordStruct); {这同上一句}

ShowMessageFmt('$%x', [ByteStruct.b1]); //$11

ShowMessageFmt('$%x', [ByteStruct.b2]); //$22

ShowMessageFmt('$%x', [ByteStruct.b3]); //$33

ShowMessageFmt('$%x', [ByteStruct.b4]); //$44

end;

end.