Reference resources ：http://www.cnblogs.com/huangjacky/archive/2009/12/21/1628833.html

An array is a collection of data with the same characteristics , That is, the type of each element must be the same , Of course, in other languages with weak grammar , The elements of an array can be various , Example

var
A : Array[0..2] of Integer;
begin
A := 1;
a := 1.0; // It's wrong here , Because every element has to be Integer type
end;

Delphi The classification of arrays in

1. Fixed length and indefinite length

Fixed length array

A fixed length array is defined at the time of declaration , The back can't be changed , And in fixed length arrays , The starting sequence number does not have to be from 0 Start , You can make it yourself , for example

var
A : Array[2..3] of Integer;
begin
A := 1;
SetLength(A,3); // There will be mistakes here , Because fixed length arrays can't be reallocated
end;

We can see from the above that the starting number is 2, But the step size is 1, It can't be changed . Why do we see a lot of arrays start with 0 Well ？ It's just a habit .

Let's look at a special usage

type
THuangJacky = (hjA, hjB, hjC);
const
// usage 1
B : Array[0..2] of string = ('A', 'B', 'C');
// usage 2
C : Array[THuangJacky] of string('A', 'B', 'C');
var
H : THuangJacky;
S :String;
begin
S := B[Ord(H)]);
S := C[H];
//B[H] and C They all make mistakes
end;

As can be seen from the above example Any ordinal type can be used as the ordinal number of an array , But when we use it, the ordinal number must be the declared ordinal type , That's why the above code comments only write two kinds of errors

Indefinite length arrays

Indefinite length arrays ： The dynamic array , That is to say The length of the statement was not stated , It must be declared before use , Length can be redistributed , The serial number must be from 0 Start , Example

var
A : Array of Integer; // A possible definition of a fixed length array is A :Array[0..10] of Integer
begin
SetLength(A, 3); // Array has 3 Elements
A := 1;
A := 2;
A := 3;
//A No, , Because only 3 Elements SetLength(A, 4); // If it gets longer , Add the following elements directly
A := 4; // Now add a fourth element , And the first three elements are still those three SetLength(A, 3); // If the length gets shorter , The excess will be removed
// Now? A period
end;

occasionally , You have to set the length first , In assignment , so much trouble , Now let's introduce a one-stop trick

type
TA = Array of Integer;
var
A : TA;
begin
A := TA.Create(1, 2, 3);
// Please don't do this in Delphi 7 The use of // After using the above method ,A :=1, A := 2, A:=3
end;

2. One dimension and many dimensions

All the previous examples , We're talking about one-dimensional arrays , To make a matrix （ Multidimensional arrays ） What do I do ？

var
A : Array[0..2, 0..2] of Integer;
B : Array[0..2] of Array[0..2] of Integer;
begin
A[0, 0] := 1;
B[0, 0] := 1;
end;

Both methods are possible , The following introduces the indefinite length array in the two-dimensional array

var
B : Array of Array of Integer
begin
// Set up a 3*3 Matrix
SetLength(B, 3, 3); // If you need to implement a dentate array , You have to do it like this
SetLength(B, 3);
SetLength(B, 1);
SetLength(B, 2);
SetLength(B, 3);
end;

Next, I'll introduce some common functions about arrays

1. Copy function

var
A, B : Array[0..1] of Integer;
begin
A := 1;
A := 2;
B := A;
B :=2;
ShowMessageFmt('A0:%D, B0:%D', [A, B]); //A0:1,B0:2
end;

This effect is what we want , There seems to be nothing to say , But if it's a dynamic array ？

var
A, B : Array of Integer;
begin
SetLength(A, 2);
SetLength(B, 2);
A := 1;
A := 2;
B := A;
B := 2;
ShowMessageFmt('A0:%D, B0:%D', [A, B]); //A0:2, B0:2
// Obviously changed B After the value of , Yes A It also has an impact , therefore B and A There's a connection between
end;

What now? ？A and B Linked to an address , Now we can actually use Copy function , We can solve this problem

var
A, B : Array of Integer;
begin
SetLength(A, 2);
SetLength(B, 2);
A :=1;
A :=2;
B := Copy(A); // The entire array is assigned a value
B := Copy(A, 0, 2); // Selective replication
B := 2;
ShowMessageFmt('A0:%D,B0:%D', [A, B]); // A0:1,B0:2
end;

2. The serial number is related to

function Low() and High() trustworthy , But here's the thing , The type they return is the type of the ordinal number of our array , Not all of them are Integer, As in the previous example THuangJacky

var
A : Array of array of string;
I, J : Integer;
begin
SetLength(A, 10);
for I := Low(A) to High(A) do
begin
SetLength(A[I], I);
for J := Low(A[I]) to High(A[I]) do
A[I, J] := IntToStr(I) + ',' + IntToStr(J) + ' ';
end
end;
end.

3. The length of the array

Length() Function returns Integer type

var
A : Array of Integer;
begin
SetLength(A, 2);
Length(A);
end.

From the above example, we can see that ： A constant length array variable is a variable , So you can use it directly := To assign a value , And a dynamic array variable is a pointer , If used := To assign a value , The two variables are linked together

var
A :Array[0..2] of Integer;
B :Array of Integer;
begin
ShowMessageFmt('A:%8x, A:%8p', [Integer(@A), @A]); // equally , From the address, this array control is on the stack
SetLength(B, 3);
ShowMessageFmt('B:%8p, B:%8p', [B, @B]); // equally , This data space is on the heap
end

We see A You have to get an address to get in touch with A It's the same as the address , So in other words A Namely A;

and B Directly with B It's the same as taking the address , in other words B Namely B The address of

The distribution of arrays in memory ： Continuously distributed , The interval is the size of each element

var
A: Array[0..2] of Integer;
B: Array of Integer;
begin
A := 123;
// from A That is to say A Go down the top of your address 4 The first is directly A
ShowMessageFmt('A:%D, Direct value :%D',[A, PInteger(Integer(@A)+4)^]);
// equally , All are 123
SetLength(B, 3);
B := 88;
// from B Go down 8 Bytes is B
ShowMessageFmt('B:%D, Direct value :%D',[B,PInteger(Integer(B)+8)^]);
end;

But the structure of dynamic array is very similar to that of character

 The offset -8 -4 0~Length* Elements Content 32 Number of bit references Element number The actual content

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