C and Pointers to learning notes (3)

Chapter 8 Arrays

1. Arrays and pointers

The array name is a pointer constant , which is the address of the 1 element of the array.

int a[10];  int b[10]; int *c;

(1) c = & A[0]; &a[0] represents a Pointer to an array of 1 elements.

(2) C=a; with the C = & A[0]; equivalence

(3) B = A; illegal , you cannot use an assignment to copy all elements of an array to another array, you must use a loop to copy one element at a time.

(4) a = C; illegal ,a is a pointer constant, and C is a pointer variable.

2. the subscript reference and the indirect access are identical.

Array[subscript] <==> * (array + (subscript)) ( fully equivalent )

eg:int array[10];

int *ap=array+2;

(1) AP : <==> array + 2 <==> &array[2]

(2) *ap : <==> array[2] <==> * (array+2)

(3) AP [0] : <==> * (AP + (0)) <==> array[2]

(4) AP + 6 : <==> array + 8 <==> &array[8]

(5) *ap + 6 : <==> array[2]+6

(6) * (AP + 6) : <==> array[8]

(7) AP [6] : <==> array[8]

(8)ap[-1] : <==> array[1]

(9) 2[array] : <==> * ((array)) <==> * (array + 2)

3. representation of string constants

(1) char message1[] = "Hello"; Initializes an element of a character array

(2) Char *message2 = "Hello"; true string constants

The pointer constant message2 is initialized to the storage location that points to the string constant.

1. 4. sequential storage of array elements

eg : int array [3][6];

Array:

　　

5. int matrix [3][10];

Matrix the value of the name is a pointer to its first 1 elements , so the matrix is a pointer to an array containing a total of ten integers.

(1) * (Matrix + 1) : pointer to integral type. Sub-array the address of the 1 element .

(2) * (Matrix + 1) +5 : The address of the 6 element .

(3)* (* (Matrix + 1) + 5):<==> Matrix [1][5]

6. Pointers to arrays

int vector[10], *vp = vector; correct

int matrix[3][10], *mp = Matrix; Error

Because thematrix is not a pointer to an integral type, it is a pointer to an array of integers .

Int (*p) [ten]; declares a pointer to an array of integers, andp is a pointer to an array of integral types

int (*p) [Ten] = Matrix; // declaration + initialization

Point to the 1 integral elements of the matrix:

(1) int *pi = &matrix [0][0];

(2) int *pi = matrix[0];

7. Pointer compatibility

(1) int *pt;

int (*PA) [3];

int AR1 [2] [3];

int AR2 [3] [2];

int **p2;

The

PT = & AR1 [0] [0];

PT = ar1 [0];

PT = AR1; illegal ,pt points to an int value , while ar1 points to 3 int values constitute the Array

PA = ar1; all point to Int[3]

PA = ar2; illegal ,pa points to an array of 3 int , and ar2 points to a 2 a int Array of Components

P2 = &pt; all point to int *

*P2 = ar2 [0]; The *P2 type is a pointer to int , so it is compatible with ar2 [0]

P2 = ar2; illegal ,p2 is pointer to pointer,ar2 is pointed by 2 int A pointer to the array that the value consists of.

Therefore,the P2 and ar2 types are different .

(2) It is legal to assign the address of a constant or very data to a pointer to a constant . Only the address of a very large amount of data can be assigned to a normal pointer .

int *p1;

const int *P2;

const int **PP2;

P1 = p2; illegal , assigning a const Pointer to a non- const pointer

P2 = p1; legal, assigning a non- const pointer to a const pointer, provided that only one layer of indirection is performed

PP2 = &p1; illegal , assigning a non- const pointer to a const pointer

C and Pointers to learning notes (3)