Shulou(Shulou.com)06/01 Report--

In this issue, the editor will bring you about how to make clever use of array types and array pointers. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

Through the access structure, some methods of using array types and pointers are slowly introduced; the test contents and results of six small examples are the same.

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

Button6: TButton

Procedure Button1Click (Sender: TObject)

Procedure Button2Click (Sender: TObject)

Procedure Button3Click (Sender: TObject)

Procedure Button4Click (Sender: TObject)

Procedure Button5Click (Sender: TObject)

Procedure Button6Click (Sender: TObject)

End

Var

Form1: TForm1

Implementation

{$R * .dfm}

Type {define structure and structure pointer first}

PMyRec = ^ TMyRec

TMyRec = record

F1: Char

F2: Word

End

{it is convenient to store or read / write structures in static arrays.

Procedure TForm1.Button1Click (Sender: TObject)

Var

ArrRec: array [0..2] of TMyRec

I: Integer

Begin

{write}

For I: = 0 to 2 do

Begin

ArrRec.F1: = Chr (iTun65)

ArrRec.F2: = (iTun1) * 10

End

{read}

For I: = 0 to Length (ArrRec)-1 do

ShowMessageFmt ('% s,% dwells, [ArrRR [I] .F1, ArrRR [I] .F2])

End

{this only defines a piece of memory, does not use the concept of array, it is a bit troublesome.

Procedure TForm1.Button2Click (Sender: TObject)

Var

Buf: PMyRec

Begin

GetMem (buf, SizeOf (TMyRec) * 3); {request memory}

{write}

Buf ^ .F1: ='A'

Buf ^ .F2: = 10

Inc (buf); {to next}

Buf ^ .F1: ='B'

Buf ^ .F2: = 20

Inc (buf)

Buf ^ .F1: ='C'

Buf ^ .F2: = 30

Dec (buf, 2); {back to start}

{read}

ShowMessageFmt ('% s,% dumped, [BUF ^ .F1, BUF ^ .F2])

Inc (buf); {to next}

ShowMessageFmt ('% s,% dumped, [BUF ^ .F1, BUF ^ .F2])

Inc (buf)

ShowMessageFmt ('% s,% dumped, [BUF ^ .F1, BUF ^ .F2])

Dec (buf, 2); {back to start}

FreeMem (buf); {release memory}

End

{you can define an array type for the structure}

Procedure TForm1.Button3Click (Sender: TObject)

Type

TArr = array of TMyRec

Var

Buf: PMyRec

I: Integer

Begin

GetMem (buf, SizeOf (TMyRec) * 3)

For I: = 0 to 2 do

Begin

TArr (buf) [I] .F1: = Chr (iTun65)

TArr (buf) [I] .F2: = (iTun1) * 10

End

For I: = 0 to 2 do

ShowMessageFmt ('% s,% dwells, [TArr (buf) [I] .F1, TArr (buf) [I] .F2])

FreeMem (buf)

End

{it is OK to use dynamic array directly.

Procedure TForm1.Button4Click (Sender: TObject)

Var

Arr: array of TMyRec

I: Integer

Begin

SetLength (Arr, 3)

For I: = 0 to 2 do

Begin

Arr [I] .F1: = Chr (iTun65)

Arr [I] .F2: = (iTun1) * 10

End

For I: = 0 to 2 do

ShowMessageFmt ('% s,% dwells, [Arr [I] .F1, Arr [I] .F2])

End

{use an array pointer to an element, which is very common}

Procedure TForm1.Button5Click (Sender: TObject)

Type

PArr = ^ TArr

TArr = array [0.. 0] of TMyRec

Var

Buf: PArr

I: Integer

Begin

GetMem (buf, SizeOf (TMyRec) * 3)

For I: = 0 to 2 do

Begin

BUF ^ [I] .F1: = Chr (iTun65)

Buf ^ [I] .F2: = (iTun1) * 10

End

{you can't read or write in this way, that is, a constant in [] cannot be more than 0, but you can use a variable}.

{this is also easy to understand, because constants are compiled directly into the code, and the compiler does not know that the array will be larger until memory is allocated.

{the next method is needed to solve this problem.

/ / buf [0] .F1: ='A'

/ / buf [0] .F2: = 10

/ / buf [1] .F1: ='B'

/ / buf [1] .F2: = 20

/ / buf [2] .F1: ='C'

/ / buf [2] .F2: = 30

For I: = 0 to 2 do

ShowMessageFmt ('% s,% dumped, [buf [I] .F1, BUF [I] .F2])

FreeMem (buf)

End

{use a very large array pointer, as Delphi's TList class does}

Procedure TForm1.Button6Click (Sender: TObject)

Type

PArr = ^ TArr

TArr = array [0.100000] of TMyRec; {Don't worry about the memory explosion, we only use its pointer when using it.

Var

Buf: PArr

I: Integer

Begin

GetMem (buf, SizeOf (TMyRec) * 3)

For I: = 0 to 2 do

Begin

BUF ^ [I] .F1: = Chr (iTun65)

Buf ^ [I] .F2: = (iTun1) * 10

End

{unlike the previous example, the following code can also}

/ / buf [0] .F1: ='A'

/ / buf [0] .F2: = 10

/ / buf [1] .F1: ='B'

/ / buf [1] .F2: = 20

/ / buf [2] .F1: ='C'

/ / buf [2] .F2: = 30

For I: = 0 to 2 do

ShowMessageFmt ('% s,% dumped, [buf [I] .F1, BUF [I] .F2])

FreeMem (buf)

End

End.

The above is the clever use of array types and array pointers shared by the editor. If you happen to have similar doubts, please refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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